XXXVII International Symposium on Dynamical Properties of Solids (DyProSo2019)


The 37th International Symposium on Dynamical Properties of Solids - DyProSo 2019
Ferrara 8-12 September, 2019 
DyProSo is an international biannual research meeting on functional properties of condensed matter resulting from elementary excitations, molecular motions, transport processes and other dynamic phenomena occurring in many body systems. Experimental evidences and investigations, as well as theoretical models and predictions, are particularly appropriate.
A special purpose of the Symposium is to trigger a scientific dialogue between young and experienced researchers working on the dynamics of materials.
The 37th DyProSo will be held in Ferrara, a historical city in northern-east Italy, founded as a Bizantine castrum in the VI century and undergoing a time of splendor and international attractiveness during the dukedom ruled by the Estense family in the XV-XVI centuries.
It has a magnificent Castle in the city center and a 13 km long track on the walls all around the ancient town, addressed by the Poet:
while stranger wonder o’er thy unpeopled wall” (Lord Byron).
Apart from usual invited and contributed lectures and posters there will be also room for short scientific communications (intended especially for students). Following the traditions of DyProSo there will be no parallel sessions.
Under the auspices of:
Sponsored by:

    • Registration
    • Opening Cerimony
      • 1
        Welcome and Introduction by the conference chair Prof. Federico Montoncello and Prof. Vincenzo Guidi
      • 2
        Breaking the attosecond limit - From spin metamaterials to novel THz applications
        Speaker: Markus Münzenberg (University of Greifswald Germany)
    • 6:30 PM
      Welcome Buffet
    • Registration
    • Keynote talk
      • 3
        Exploring the third dimension in Magnonic Crystals

        Magnonic crystals (MCs) are materials with periodically modulated magnetic properties where the spin waves (SWs) band structure consists of intervals of allowed SW frequencies and forbidden gaps in which there are no allowed magnonic states.
        In the recent past, most of the studies have been focused on planar nanostructures where the magnetic constituents have the same thickness, while, to the best of our knowledge, there are no reports of SW band structure in 3D MCs. This is mainly due to the difficulties associated with the fabrication of thickness modulated nano-elements by conventional nanofabrication techniques which require multilevel exposure process and alignment between successive fabrications steps.
        Very recently, we proposed a new class of MCs constituted by closely packed thickness-modulated Permalloy, Fe/Permalloy and Fe/Cu/Permalloy nanowires. We show that this kind of structures support the propagation of collective SWs in the periodicity direction, thus demonstrating that layering structure and in-plane modulation are very effective for controlling the characteristics of the magnonic band.[1]
        Another possible approach to achieve a vertical control of the spin wave band structure is to have either an array of layered magnetic elements or an array of ferromagnetic dots deposited on top of a continuous ferromagnetic film. I will review the properties of the spin wave band structure, studied by wavevector-resolved Brillouin light scattering, in dense arrays of Py/Cu/Py nanowires [2,3] and 2D array of elliptical Py/Pt nanodots arranged into dense chains over the surface of a 20 nm thick Py continuous unpatterned film.[4] Particular emphasis is given to the reconfigurable dynamic response of these systems.
        Finally, I will present some recent results on three-dimensional model of periodic meander-shaped ferromagnetic films and vertically coupled structures.

        [1] G. Gubbiotti et al., “Collective spin waves on a nanowire array with step-modulated thickness”, J. Phys. D Appl. Phys., 47, 105003 (2014)
        [2] G. Gubbiotti et al., “Reprogrammable magnonic band structure of layered permalloy/Cu/permalloy nanowires”, Phys. Rev. B 97, 134428 (2018).
        [3] G. Gubbiotti et al. “Interplay between intra- and inter-nanowires dynamic dipolar interactions in the spin wave band structure of Py/Cu/Py nanowires”, Sci. Rep. 9, 4617 (2019)

        [4] P. Graczyk et al, “2D re-programmable magnonic crystal with vertical control of the spin wave dynamics: Py film decorated with array of elliptical nanodots”, Phys. Rev. B. 98, 174420 (2018)

        Speaker: Gianluca Gubbiotti (Istituto Officina dei Materiali - CNR)
    • Morning Session 1: Chair: Paolo Vavassori (CIC nanoGUNE, Donostia, Basque Country (Spain))
      • 4
        Direct detection of multiple backward volume modes in yttrium iron garnet at micron scale wavelengths

        Spinwave propagation in yttrium iron garnet (YIG) films has a long history but has recently attracted renewed attention due to the observation of an unusual coherent phenomenon in a heavily pumped magnon gas in the backward volume geometry where the spectrum displays a minimum. The effect has been termed Bose condensation or, from a more classical perspective, a Rayleigh-Jeans condensation. The time dependence of the observed behavior has recently been simulaed and shown to arise from a dynamic equilibrium state of a classical magnon gas interacting through three and four magnon scattering processes.

        The measurements cited above utilized the Brillouin scattering technique which has the advantage allowing studies over a broad spectral range, but for which the resolution is limited. To better understand the properties of magnons in the vacinity of the minimum in the spectrum (where the condensation occurs) we have patterned a set of wave-vector-specific, multi-element, ”ladder” antennas, with which we can directly couple spin waves with micron and submicron wavelengths to a microwave generator and determine the resulting absorption. Our mesurements, which are shown in the attached figure, were carried out on a 2.84 micron film and have resolved the dispersion relations of multiple (ten or more depending on the wavelength) low lying backward volume modes for wavelengths of 10, 3, 1 and 0.6 microns. Overall the data are in excellent agreement with theoretical predictions based on a Heisenberg model Hamiltonian. Data are also compared with solutions of Landau-Lifshitz equation that include both dipolar and exchange effects.

        We will also report our recent experiments in which we use our one micron antenna to detect coherent spin waves at the minimum which arise via a Suhl two magnon decay processes where we pump at twice the detecteed frequency; this is the first time such modes have been detected to our knowledge. Other parametric pumping experiments will also be described.

        The techniques developed in this work now facilitate the characterization of spin waves at length scales limited only by available lithography and with a spectral resolution that greatly exceeds that of Brillouin scattering.

        Speaker: John B. Ketterson (Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA.)
      • 5
        Dimensionality effects and phase transition dynamics in spintronics materials as seen by X-ray electron spectroscopies

        Hole-doped rare-earth manganites, like La0.66Sr0.33MnO3 (LSMO), display peculiar phenomena such as colossal magnetoresistance and half-metallicity, originating from the competition between charge, spin, and orbital order parameters [1]. Optimally doped LSMO thin films can be used to realize fully spin polarized currents (the spin polarization at the Fermi level reaches about 100% for T<TCurie [2]), a feature which, combined with the ferromagnetic order that persists up to about 350 K [3] render such system a most technologically attractive material for spintronics. . Hard X-ray PhotoElectron Spectroscopy (HAXPES) extends the probing depth of PES to the bulk of the solid (tens of nm), and therefore does not suffer of the modification induced by the surface electronic relaxation, revealing specific bulk-only features responsible of electron and metallic properties [4,5]. Furthermore, pump-probe HAXPES experiments reveal spin-dynamics extending up to several hundreds of picoseconds after the IR pumping. By comparison with all-optical techniques we are able to attribute the observed quenching to a collapse of magnetic order related to double exchange and half-metallicity of the system [6].
        [1] Y. Tokura et al. J. Magn. & Magn. Mater. 200, 1 (1999).
        [2] G.M. Müller et al. Nat. Mat. 8, 56 (2009)
        [3]J.-H. Park, et al. Nature, 392, 794 (1998).
        [4] K. Horiba et al. Phys. Rev. B 71, 155420 (2005).
        [5] T. Pincelli, et al., Nat. Commun. 8, 16051 (2017).
        [6] M. Oura, et al., Synchrotron Radiation News, July issue, 36-41 (2018)

        Speaker: Giancarlo Panaccione (CNR-IOM)
      • 6
        Spin wave modes in a cylindrical nanowire in crossover dipolar-exchange regime

        The confinement in magnetic structure is responsible not only for the quantization of spin wave modes due to geometrical constraints but also determines the dipolar interactions. Although the magnetic wires were already [1] broadly investigated, some of their dynamical properties, like: (anti)crossing between the spin wave modes and the impact of the magnetic field on the spin wave spectrum, still need to be explored. In our studies [2] we identify the dispersion brunches and their (anti)crossing in crossover dipolar-exchange regime by plotting the spatial profiles of spin wave amplitudes and magnetostatic potential. We also check how we can tune the spectrum of the modes by application of the external magnetic field and how it affects the modes and their dominating type of interaction. We use two approaches for solving the Landau-Lifshitz equation to investigate the spin wave dynamics: semi-analytical calculations and numerical computations based on the finite element method.
        [1] R. Arias and D. Mills, Phys. Rev. B 70, 094414 (2004)
        [2] J. Rychły, V. S. Tkachenko, J. W. Kłos, A. Kuchko, and M Krawczyk, J. Phys. D: Appl. Phys. 52, 075003R (2018).

        The research has received funding from the National Science Centre of Poland under grants No. UMO-2017/24/T/ST3/00173, No.2016/21/B/ST3/00452.

        Speaker: Jaroslaw Klos (Faculty of Physics, Adam Mickiewicz University in Poznań, Poznań, Poland )
      • 7
        Edge modes in the switching mechanism of finite chains of macrospins

        We study transitions of 1D systems of macrospins between their equilibrium configurations under a uniform magnetic field and under variations of the distances of the macrospins in such chains. A magnetic field opens a gap at the Brillouin zone border, giving room to bound edge states. If the number of macrospins in the chain is odd, two bound states, symmetric and antisymmetric, appear in the gap for the magnetic field parallel to the magnetization of the end macrospins and the instability is driven by a bulk soft mode. If the field is oriented antiparallel to the end macrospins no bound modes appear in the gap. In turn the instability involves softening of edge bound states as illustrated in Fig.1. The even-odd alternation of this behaviour will be presented, as well as the effect of variations of the macrospins mutual distances.

        Speaker: Dominika Kuźma (Institute of Nuclear Physics Polish Academy of Sciences, PL-31342 Krakow, Poland)
      • 8
        Domain structure and magnetization reversal mechanism in Co/Pd nanopatterned multilayer

        Fabrication and modeling of patterned thin films with perpendicular magnetic anisotropy rise great interest due to their wide applications in magnetic storage, sensors and magnonic crystals. A good representative of such systems are well-ordered arrays of magnetic antidots and dots based on Co/Pd multilayers, where magnetic reversal mechanisms strongly depend on the array geometry [1, 2]. We attempt to understand and reproduce the observed magnetic properties and domain structure appearing in the arrays by micromagnetic simulations performed using Mumax3 software [3]. In particular, changes in coercivity field, magnetic anisotropy constant and magnetic domain arrangement were studied and correlated with symmetry and size of nanostructures. The domain pattern simulations shed light on the details of formation the Néel domain walls, as compared to Bloch walls, depends on the distances between the antidots. The calculations show how edge effects, defects and inhomogeneity affect magnetization reversal and domain wall pinning mechanism, which helps to design similar patterned systems with the specific magnetic properties.

        Speaker: Paweł Sobieszczyk (Institute of Nuclear Physics PAN)
    • 10:40 AM
      Coffee Break
    • Invited Talk
      • 9
        Magneto-plasmonic nanostructures and crystals

        Magneto-plasmonic nanostructures and crystals

        Speaker: Paolo Vavassori (CIC nanoGUNE, 20018 San Sebastian and IKERBASQUE Basque Foundation for Science, 48013 Bilbao(Spain))
    • Morning Session 2: Chair: Gianluca Gubbiotti (CNR-IOM - Istituto Officina dei Materiali, Perugia (Italy))
      • 10
        Measuring interfacial Dzyaloshinskii-Moriya interaction: a review

        Topology is known to stabilize rather exotic states in condensed matter and in magnetic materials. A recent example is the formation of particle-like excitations of continuous fields, as predicted by Skyrme. These so called skyrmions occur in presence of inversion symmetry breaking and indirect exchange, both favouring chiral magnetic structures via the Dzyaloshinskii-Moriya Interaction (DMI) [1,2]. Recently, the DMI received broad attention from the magnetism community as it was found to occur in systems appealing for spintronic applications composed of a heavy metal (HM) layer and an ultrathin ferromagnetic (FM) film with perpendicular magnetic anisotropy (PMA). Here the inversion symmetry breaking is induced by the interface and the exchange interaction is mediated by the spin-orbit coupling in the HM layer. Chiral domain walls and skyrmions are emerging as promising information carriers for future spintronic technologies, as they can be driven by electric currents with an unprecedented level of efficiency [3]. A measure for the stability of chiral magnetic structures and the strength of the DMI is the related energy coefficient D [2]. Although DMI-based phenomena have created an extremely active research field, an established and reliable method to measure D is still lacking. As a matter of fact, a lot of disagreement is currently present in the literature, especially regarding measurements of small DMI (D<0.5mJ/m2). Not only different measuring techniques are found to provide contradictory values for D, but controversies are also present when utilizing the same method on nominally identical stacks. We present here a review of interfacial DMI measurements, considering not only the different measurement techniques as domain wall based [4,5] and spin wave based [6] measurements, but also different compositions of the stacks investigated (e.g. FM: Co, CoFeB; HM: Pt, Ta, Ir, W). We try to clarify the differences of the various techniques describing their advantages and limitations and define a set of rules to be able to compare the data, quantitatively define the role of HM layer, considering its thickness, the production methodology, the annealing, etc. We also aim to introduce a standard coordinate system for the experimental quantities in order to define uniquely the sign of D.
        [1] I. Dzyaloshinskii, Sov. Phys. JETP 5, 1259 (1957).
        [2] T. Moriya, Phys. Rev. 120, 91 (1960).
        [3] S. Parkin and S.-H. Yang, Nat. Nanotechnol. 10, 195 (2015).
        [4] S. Emori et al., Nat. Mater. 12, 611 (2013).
        [5] S.G. Je et al., Phys. Rev. B 88, 214401 (2013).
        [6] K.W. Moon et al., Sci. Rep. 5, 9166 (2015).

        Speaker: Michaela Kuepferling (Istituto Nazionale di Ricerca Metrologica)
      • 11
        Reciprocal relation between spin Peltier and spin Seebeck effects

        In recent times, the interaction between magnetization and heat currents in a magnetic material has gained a renewed interest thanks to the observation of the spin Seebeck effect (SSE) [1,2]. The SSE is the spin counterpart of the Seebeck effect that corresponds to the generation of a pure magnetization current in a magnetic insulator as consequence of a thermal gradient. This is electrically detected by means of the inverse spin Hall effect [3], that rises in a high spin orbit coupling heavy metal deposited on the magnetic insulator. As in the ordinary thermoelectricity, the SSE has its reciprocal effect that is the spin Peltier effect [4,5]. In this work we provide an experimental proof of the reciprocal relations between SSE and SPE [6,7] in a single bulk sample of yttrium iron garnet (YIG) covered by a platinum thin film. For both the SSE and the SPE experiments, we employ a measurement system designed for the detection of heat currents exchanged between the thermal reservoirs and the sample under test. The sample-specific value for the characteristics of both effects measured on the present YIG/Pt bilayer is (6.2 ± 0.4) × 10−3 KA−1 at room temperature, that corresponds to the spin-analogue of the Thomson relation between thermoelectric effects.
        [1] Uchida, K. et al. Appl. Phys. Lett. 97, 172505 (2010).
        [2] Bauer, G. E. W., Saitoh, E. & van Wees, B. J. Nature materials 391, 11 (2012).
        [3] Saitoh, E. et al. Appl. Phys. Lett. 88, 182509 (2006)
        [4] Flipse, J. et al. Phys. Rev. Lett. 113, 027601 (2014)
        [5] Daimon, S. et al. Phys. Rev. B 96, 024424 (2017)
        [6] Basso, V. et al. IEEE Magnetics Letters 9 (2018): 1-4

        Speaker: Alessandro Sola (Istituto Nazionale di Ricerca Metrologica)
    • Invited Talk
      • 12
        Time-resolved investigations and biotechnological applications of plasmonic nanostructures

        Plasmonics exploits the collective motion of conduction electrons in metals (plasmons), thus
        enabling light to couple with nanoscale objects, with the consequent generation of a plenty of
        novel and unexpected optical effects and functionalities. Plasmonic nanostructures have been
        deeply studied in the last decade due to their crucial impact on several areas of nanoscience
        and nanotechnology. Their unrivalled capability to squeeze light well beyond its diffraction
        limit, leading to extremely confined and enhanced electromagnetic fields on the nanoscale at
        optical frequencies, is of great interest for the prospect of real-life applications, such as
        energy harvesting and photovoltaics, wave-guiding and lasing, optoelectronics, fluorescence
        emission enhancement, plasmon-assisted bio-interfaces and nanomedicine. In this
        framework, traditional studies of the resonant behavior of plasmonic nanoantennas rely on
        standard intensity detection schemes. Up to date, the temporal dynamics of plasmonic
        nanoantennas remains challenging. In the first part of the talk we will show that, by
        combining femtosecond multi-THz time-domain spectroscopy and high-resolution confocal
        microscopy, it is possible to measure full time- and field-resolved response of single
        plasmonic antennas (see Fig. 1) [1]. In the second part of the talk, we will then show
        practical applications of plasmonic nanostructures for molecular sensing [2,3], single cell
        enhanced spectroscopy [4-6], optical trapping [7] and enhanced resonant energy transfer [8].
        [1] M. P. Fischer, N. Maccaferri, K. Gallacher, J. Frigerio, G. Pellegrini, G. Isella, A.
        Leitenstorfer, D. J. Paul, P. Biagioni, D. Brida, in preparation (2019).
        [2] R. Verre, N. Maccaferri, K. Fleischer, M. Svedendahl, N. Odebo Länk, A. Dmitriev, P.
        Vavassori, I. V. Shvets, M. Käll Nanoscale 8, 10576 (2016).
        [3] P. Ponzellini, X. Zambrana-Puyalto, N. Maccaferri, L. Lanzanò, F. De Angelis, D. Garoli
        Nanoscale 10, 17362 (2018).
        [4] M. Ardini, J.-A. Huang, C. S. Sánchez, M. Z. Mousavi, V. Caprettini, N. Maccaferri, G.
        Melle, G. Bruno, L. Pasquale, D. Garoli, F. De Angelis Sci. Rep. 8, 12652 (2018).
        [5] V. Caprettini, J.-A. Huang, F. Moia, A. Jacassi, C. A. Gonani, N. Maccaferri, R.
        Capozza, M. Dipalo, F. De Angelis Sci. Adv. 5, 1800560 (2018).
        [6] J.-A. Huang, V. Caprettini, Y. Zhao, G. Melle, N. Maccaferri, L. Deleye, X. ZambranaPuyalto, M. Ardini, F. Tantussi, M. Dipalo, F. De Angelis Nano Lett. 19, 722 (2019).
        [7] G. C. Messina, X. Zambrana-Puyalto, N. Maccaferri, D. Garoli, F. De Angelis
        arXiv:1903.03865 (2019).
        [8] X. Zambrana-Puyalto N.Maccaferri, P. Ponzellini, G. Giovannini, F. De Angelis, D.
        Garoli Nanoscale Advances, in press (2019).

        Speaker: Nicolò Maccaferri (University of Luxembourg,)
    • 12:30 PM
    • Invited Talk
      • 13
        Terahertz-Driven Phonon Upconversion in SrTiO3

        Direct manipulation of the atomic lattice using intense long-wavelength laser pulses has become a viable approach to create new states of matter in complex materials. Conventionally, a high frequency vibrational mode is driven resonantly by a mid-infrared laser pulse and the lattice structure is modified through indirect coupling of this infrared-active phonon to other, lower frequency lattice modulations. Here, we drive the lowest frequency optical phonon in the prototypical transition metal oxide SrTiO$_3$ well into the anharmonic regime with an intense terahertz field. We show that it is possible to transfer energy to higher frequency phonon modes through nonlinear coupling. Our observations are carried out by directly mapping the lattice response to the coherent drive field with femtosecond x-ray pulses, enabling direct visualization of the atomic displacements [1]

        [1] M. Kozina, M. Fechner, P. Marsik, T. van Driel, J. M. Glownia, C. Bernhard, M. Radovic, D. Zhu, S. Bonetti, U. Staub, and M. C. Hoffmann, Nature Physics 15, 387–392 (2019)

        Speaker: Stefano Bonetti (Ca' Foscari University of Venice)
    • Afternoon Session 1: Chair: Jiri Kulda (Institut Laue-Langevin, Grenoble (France))
      • 15
        Spin-lattice coupling in the quantum spin ice candidate Tb2Ti2O7 revealed by THz spectroscopy

        In geometrically frustrated magnetism, the very nature of the ground state of Tb2Ti2O7, has remained a long standing conundrum. In this pyrochlore material, no conventional spin-ice or long-range magnetic order is stabilized, even at very low temperatures. Quantum fluctuations are suspected of being at the origin of such an exotic quantum phase, yet so far has lacked conclusive evidence. Using high-resolution synchrotron-based terahertz spectroscopy, we have probed the lowest energy excitations of Tb2Ti2O7. It is revealed that a double hybridization of crystal-field-phonon modes is present across a broad temperature range from 200 k down to 6 K [1]. This so called vibronic process affects the electronic ground state that can no longer be described solely by electronic wave functions. We will present here new results obtained down to 250 mK in the exotic magnetic phase.

        [1] E. Constable et al, Physical Review B 95, 020415 (R) 2017

        Speaker: Sophie De Brion (Institut Néel)
    • Invited Talk
      • 16
        Resonant Inelastic X-ray Scattering Study of Excitations in Cuprate Superconductors

        The mechanism of high-TC superconductivity in cuprates remains an unsolved question since its discovery in 1986. Answering the question of its microscopic origin turns out to be a great challenge, complexity arises from the coexistence of several phases along with the superconductivity. While it has been argued that spin fluctuations may be crucial for forming superconductivity [1], abundant experimental observations also demonstrate a strong electronic coupling to the lattice [2]. Although electron-phonon coupling may not be the main origin of the Cooper pairing, its role across the phase diagram is still controversial, particularly in the under-doped region [3]. A direct way to probe the electron-phonon coupling has emerged thanks to the recent progress made in high resolution Resonant inelastic X-ray scattering (RIXS), which now allows to resolve phonons [4, 5]. Theoretical studies suggested that the RIXS phonon cross-section directly reflects the momentum-dependent electron-phonon coupling strength [6]. In this talk, we will focus on the dynamical properties of the under-doped cuprate Bi2Sr2CaCu2O8+δ. Low energy excitations were investigated using RIXS at the Cu L3-edge with an energy resolution of 40-45 meV [5]. In the quasi-elastic region, an incommensurate charge density wave (CDW) was observed in this system, confirming its existence in this compound. In addition, this RIXS study resolved the bond-stretching phonon in the energy-momentum space. Importantly, it also revealed that the phonon dispersion changes at the CDW wave-vector indicating that the CDW unambiguously affects the lattice. RIXS measurements on another superconducting cuprate, Ca2-xNaxCuO2Cl2, will be also discussed [7].

        [1] D. J. Scalapino, Rev. Mod. Phys. 84, 1383–1417 (2012)
        [2] A. Lanzara, et al., Nature 412, 510-514 (2001) ; W. Meevasana, et al., Phys. Rev. Lett. 96, 157003 (2006)
        [3] M. K. Crawford, et al., Science 250, 1390 (1990) ; K.-P. Bohnen, et al., Europhys. Lett. 64, 104 (2003) ; F. Giustino, et al., Nature 452, 975 (2008) ; O. Rosch, et al., Phys. Rev. Lett. 92, 146403 (2004) ; M. d'Astuto, et al., Phys. Rev. B 88, 014522 (2013)
        [4] Y.Y. Peng, et al., Phys. Rev. B 92, 064517 (2015)
        [5] L. Chaix, et al., Nature Physics 13, 952-956 (2017)
        [6] L. J. P. Ament, et al., Europhys. Lett. 95, 27008 (2011) ; T. P. Devereaux, et al., Phys. Rev. X 6, 041019 (2016)
        [7] L. Chaix, et al., in preparation.

        Speaker: Laura Chaix (Institut Néel, CNRS)
    • Afternoon Session 1: Chair: Jiri Kulda (Institut Laue-Langevin, Grenoble (France))
      • 17
        Spin dynamics and phonons, insights into potential molecular qubits

        Molecular spins are characterized by an effective electronic and magnetic tunability and this is a very relevant property for quantum computation applications [1]. In particular metal complexes have unpaired electrons located in the d orbitals, whose energy can be easily tuned using proper ligands; hence, metal complexes are very promising candidate to realize qubit devices. An accurate choice of the metal centre and of the ligands is able to substantially increase the spin coherence time [2], that is the basic requirement to implement operative qubits. In this framework, the effects of molecular and lattice vibrations, or phonons, on the spin relaxation mechanisms have been the focus of increasing attention. Thanks to our multitechnique approach, based on alternative current susceptibility, EPR and TeraHertz time-domain spectroscopy, we have evidenced correlation between low energy vibrations and spin relaxation time in molecular qubits [3,4]. Moreover, we have highlighted the role of the rigidity of the molecular structure and of the crystal lattice [4], together with the overall dimensionality [5], on phonons and on the spin dynamics. These recent results are here presented for a series of vanadyl-based compounds, where an appropriate choice of the ligand structure and of the coordination geometry allow to control the spin dynamics.

        [1] A. Ghirri, Magnetochem. 3, 12 (2017).
        [2] K. Bader, Nat. Comm. 5, 5304 (2014).
        [3] M. Atzori, JACS 139, 4338 (2017).
        [4] M. Atzori, Inorg. Chem. 57, 731 (2017).
        [5] T. Yamabayashi, JACS 140, 38 (2018).

        Speaker: Stefano Benci (LENS - Università degli Studi di Firenze)
      • 18
        Investigation of phonons and magnons in [Ni80Fe20/Au/Co/Au]10 multilayers

        The properties of surface acoustic waves (fig. 1a) and spin waves propagating in magnetic [Ni$_{80}$Fe$_{20}$/Au/Co/Au]$_{10}$ multilayers (fig. 1b) on silicon substrate have been investigated by high resolution Brillouin spectroscopy [1-2]. The behavior of spin waves was studied in two experimental geometries: Backward Volume (BV) geometry and Damon-Eshbach (DE) geometry [3]. The thickness of cobalt (Co) layer was different for each sample and the influence of the layer’s thickness on the dispersion relation has been tested. The samples were decorated with non-magnetic aluminum (Al) periodic structures. The crossing of phonon and magnon dispersion relations has also been examined. Additionally, the theoretical dispersion dependences have been obtained from simulations performed with finite element method.

        Speaker: Miłosz Zdunek (Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614, Poznań, Poland)
      • 19
        Ab-initio study of the electron-phonon interaction of a single Fe adatom on the MgO/Ag(100) surface

        Controlling the magnetic moment of individual atoms is a technologically important challenge, with applications as high density storage devices. Breakthrough experimental studies have recently shown that it is possible to create stable magnetic quantum states in individual adatoms  [1–3]⁠. While the role of electronic interactions on the magnetic stability has been thoroughly investigated theoretically  [4–6]⁠, the coupling with phonons has attracted much less attention. The aim of this work is to study, via ab-initio calculations, the effect of the electron-phonon interaction (EPI) in Fe adatoms deposited on MgO/Ag(100), a benchmark system where the EPI is believed to determine to large extent its magnetic stability  [3]⁠. Here we present the calculated electronic structure and vibrational dynamics of this system, including the local vibrations of the adatom. Furthermore, we analyze the effect of the EPI on the magnetic stability via the renormalization of the electronic properties of the adatom.

        [1] F. Donati, S. Rusponi, S. Stepanow, C. Wäckerlin, A. Singha, L. Persichetti, R. Baltic, K. Diller, F. Patthey, E. Fernandes, J. Dreiser, Ž. Šljivančanin, K. Kummer, C. Nistor, P. Gambardella, and H. Brune, Science. 352, 318 (2016).
        [2] F. D. Natterer, F. Donati, F. Patthey, and H. Brune, Phys. Rev. Lett. 121, 27201 (2018).
        [3] W. Paul, K. Yang, S. Baumann, N. Romming, T. Choi, C. P. Lutz, and A. J. Heinrich, Nat. Phys. 13, 403 (2017).
        [4] N. Lorente and J.-P. Gauyacq, Phys. Rev. Lett. 103, 176601 (2009).
        [5] J. Fernández-Rossier, Phys. Rev. Lett. 102, 256802 (2009).
        [6] J. Ibañez-Azpiroz, M. D. S. Dias, S. Blügel, and S. Lounis, Nano Lett. 16, 4305 (2016).

        Speaker: Haritz Garai-Marin (Materia Kondentsatuaren Fisika Saila, Euskal Herriko Unibertsitatea UPV/EHU, 644 Postakutxatila, 48080 Bilbao, Basque Country, Spain & Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastian, Basque Country, Spain)
      • 20
        Proton momentum distributions in strong hydrogen bonds in the solid state

        Neutron Compton scattering (NCS) is a unique experimental technique made possible by the development of epithermal neutron sources, such as the ISIS source of the Rutherford Appleton Laboratory in the UK [1, 2]. Dynamic structure factors, measured in NCS, are solely determined by the nuclear momentum distribution (NMD). In the picture of purely classical nuclei, the NMD shape is determined by whole energy spectrum of the motional modes, including translational and rotational modes, followed by lattice and internal molecular vibrations. However, more and more experimental evidence has been accumulated over the years that nuclear quantum effects, such as nuclear zero point motion, delocalisation and tunnelling, determine the shapes of NMDs of lightweight isotopes such as protons and deuterons. At sufficiently low temperatures, all nuclear quantum systems are cooled down to their ground states. In this low-temperature limit, the NCS recoil peak shape for a given nucleus is proportional to the square of the absolute value of its nuclear wave function, which is dictated by the shape of the local, effective Born-Oppenheimer (BO) potential [1, 2]. Furthermore, different shapes of the BO potentials can be selected by applying Bayesian approach to fitting data obtained from an NCS experiment [3]. Such statistical tests can detect traces of self-interference of a nuclear wave function in effective BO potentials, a prerequisite of nuclear quantum tunnelling in condensed matter systems.

        Molecular crystals exhibiting strong hydrogen bonds seem as natural fit for the NCS technique. In this contribution, the results of recent NCS investigation of the solid solutions of equimolar water-phosphoric acid mixture and its deuterated counterpart, will be presented. The analysis of the NMDs, augmented with Bayesian inference methodology, reveals line-shape features characteristic for proton tunnelling in the water-H3PO4 mixture below 160 K but shows no such features in the case of the deuterated water-D3PO4 mixture. Taken together, these observations suggest the existence of the so-called tunnelling effect in the kinetics of the proton transfer below 160K, most likely involving concerted proton tunnelling along Grotthuss chains. It is the interplay between the amount of the ZPE and the height of the activation barrier for the proton transfer, which in consequence leads to a non-trivial nuclear quantum isotope effect, whereby kinetic rate constants of protons are orders of magnitude higher than those for deuterium. The presented methodology paves the way for a novel experimental screening protocol for the presence of the signatures of nuclear quantum tunnelling in condensed matter systems.

        [1] Andreani C. et al., Electron-volt neutron spectroscopy: beyond fundamental systems, Adv. Phys. (2017), 66, 1.
        [2] "Atomic Quantum Dynamics in Materials Research ", F. Fernandez-Alonso and D. L. Price Eds., Academic Press, 2017
        [3] Krzystyniak, M. et al., Nuclear dynamics and phase polymorphism in solid formic acid. Physical Chemistry Chemical Physics, (2017) 19, 9064.

        Speaker: Matthew Krzystyniak (Rutherford Appleton Laboratory, ISIS Facility, Chilton Didcot, OX 11 OQX, Oxfordshire, United Kingdom)
    • 4:05 PM
      Coffee Break
    • Poster Session
    • Keynote talk
      • 21
        The short-range order in Zr-Ti melts

        The early transition metals Zirconium and Titanium show very similar chemical and structural properties. Alloyed they compose a completely miscible system, which is the boundary binary system for many bulk metallic glasses (BMGs) and stable quasi-crystals. However, the detailed formation mechanisms of these special structures remain largely unknown and are often speculative. Here, accurate knowledge of melt properties is essential. Using electromagnetic levitation (EML), we are able to process the chemical highly reactive Zr-Ti melts over a large temperature range and glean information of the liquid. In-situ neutron diffraction shows that barely any chemical short-range order (CSRO) is present and the melt structure is dominated by topological packing. Measurements of the self-diffusivity using quasi-elastic neutron scattering (QENS) show a concentration dependent motion of Ti-atoms in the melt. We calculate the liquid dynamics using the Mode-Coupling Theory (MCT), which predicts the dynamics from the static structure in dense fluids. The results are qualitative very similar to our QENS measurements, which indicate that the topological short-range order indeed dominates a considerable impact on the atomic motion. We show that this interplay can accurately be described using MCT, which will contribute to a comprehensive understanding how short-range order affects the quasicrystal and glass formation.

        Speaker: Sandro Szabó (Heinz Maier-Leibnitz Center (MLZ) and Physics Department, Technical University of Munich)
    • Invited Talk
      • 22
        Inelastic Neutron Scattering study of Brønsted acidity and water confinement in zeolites

        Zeolites, crystalline and microporous aluminosilicates, are one of the most important groups of
        functional materials. Zeolites are widely used as solid acid catalysts in petroleum refinery and
        petrochemical industries. Zeolites can be described as microcoporous polymorphs of quartz.
        Whilst quartz is SiO2, zeolites asmit the isomorphous substitution of Si by many tetrahedrally
        coordinated atom, typically Al (Si4+ à Al3+ + H+)
        . In this way, the Si/Al ratio gives the
        number of acid sites, but not their location and strength.The catalytic properties of a zeolite
        depend strongly on its acidity, and this in turns depends on: the total number of acid sites, their
        individual strength, and their individual location. These three factors are strongly correlated.
        Geometric parameters that are defined by the location of the acid site (i.e., bond angles and
        lengths around the acid site) make a remarkable contribution to the acid strength. It was found
        that the strong acid sites have the trend to be found in relatively small micropores.[1]
        In the present work we study the zeolite LTA Si/Al= 40 (only one acid site per unit cell). The
        structure of LTA zeolite has the micropores consisting of large and small cavities. Inelastic
        neutron scattering (INS) has been used to study the acid sites of the LTA zeolite with different
        Si/Al ratios. There are two groups of bands: the first one found at 1050-1100 cm-1 that
        corresponds to the SiOH in-plane bending and another one found near 400-500 cm-1 which is
        attributed to the out-of-plane bending. These bending modes of the acid site are not no possible
        to measure with IR spectroscopy since these bands overlap with the strong bands from the
        zeolite framework. The combination of an extremely high quality of the samples and the
        sensitivity of the instrument allows to detect with high precision the acid sites of LTA Si/Al=40
        and obtain information about its position. In order to fully understand the INS spectra we
        performed ab-initio calculations [2,3].
        In addition the polar properties of zeolites can be nicely tuned by selecting the
        appropriate chemical composition and concentration of structural defects in their frameworks. In
        the present study we were particularly interested about the mechanism of water adsorption on
        small pore zeolites and the influence of the polarity of the zeolite cavities in the clustering of
        water molecules when adsorbed in confined spaces, since there is controversy on the formation
        of hydroxonium cations when water is adsorbed on acid zeolites, and in case of hydroxonium
        formation, who many water molecules participate into the hydroxonium species. The simple
        framework of the chabazite (Fig. 1left) makes this zeolite and ideal candidate for the INS study
        of adsorbed molecules with theoretical approaches in order to provide a deep understanding on
        the influence of the polarity of zeolite on the clustering of adsorbed water [4].
        References:[1] N. Katada et al., “J. Phys. Chem. C 2009, 113, 19208- 19217. [2] T. Lemishko et
        al., J. Phys. Chem. C 2016, 120, 24904−24909. [3] T. Lemishko et al., J. Phys. Chem. C 2018, 122,
        11450−11454 . [4] M. Jimémez-Ruiz et al., manuscript in preparation.

        Speaker: Monica Jimenez-Ruiz (Institute Laue-Langevin)
    • Morning Session 1: Chair: Piotr Zieliński (Institute of Nuclear Physics Polish Academy of Sciences, Cracow (Poland))
      • 23
        Advanced Diffusion Strategies for Junction Formation in Germanium

        The investigation of innovative dynamical processes for the fabrication of highly doped and
        high quality Ge layers is currently a hot topic in many applicative fields such as
        nanoelectronics, photonics and radiation detectors. Challenges that require a deep physical
        and material science investigation are: i) the high electrical activation in narrow region that
        can be obtained by out of equilibrium processes but has not to introduce lattice damage that
        may deteriorate the electrical properties. High concentration of the active dopant may
        transform germanium in a plasmonic material for sensor applications, or in an optical active
        material thanks to the direct gap transition that occurs at high doping and high strain. ii) The
        control of the amount of doping at nanoscale (deterministic doping) is fundamental to meet
        the request of nanodevices production. Traditional methods as ion implantation are difficult
        to manage due to statistical fluctuations. In particular, this task has to be solved in
        germanium to exploit such material as a high mobility material in nanoelectronic. iii) The
        preservation of the material purity during doping processes is a relevant problem especially
        when high purity germanium (HPGe) is used for gamma detector for nuclear spectroscopy
        and gamma imaging applications.
        In this talk we will present some example of our recent research on germanium to contribute
        to the above challenges. Molecular doping process i.e. the production of monolayer selfassembled source of dopants on the devices surface is a promising way toward deterministic
        doping. We recently investigate the use of both P and Sb monolayer to this aim [1]. The
        effectiveness of such monolayer as diffusion sources is investigated. A very promising way
        to obtain very high doping is pulsed laser melting (PLM), this is a highly out equilibrium
        process that melt the extreme surface of the crystal and allow for dopant diffusion into the
        melt and its incorporation during fast regrowth. The application of this method to Ge allow
        for record activation of the dopants. Finally, we investigated the contamination induced by
        this laser process in the bulk of the material and we understood that it is a very promising
        method for doping of HPGe making possible fast and cheap processing for next generation
        gamma detectors [2,3].
        [1] F. Sgarbossa et al. , Nanotechnology 29, 465702 (2018).
        [2] V. Boldrini et al. J. Phys. D: Appl. Phys. 52 035104 (2018).
        [3] G. Maggioni et al. Eur. Phys. J. A 54, 34 (2018).

        Speaker: Davide De Salvador (University of Padova)
      • 24
        On some enigmatic properties of relaxation functions

        A. Horzela$^1$, K. Górska$^1$, A. Lattanzi$^1$
        $^1$Institute of Nuclear Physics IFJ PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland

        The Debye model of dielectric relaxation provides us with the simplest shape of spectral functions, i.e. relations connecting characteristics of polarized dielectric medium and the frequency $ω$ of the polarizing electric field. An example of such a relation is $\chi(i\omega)=(1+i\omega\tau_{D})^{-1}$ which shows how the complex susceptibility $\chi(i\omega)$ depends on $\omega$ and on a single material parameter called the characteristic time $\tau_{D}$. As expected, such a spectral function transformed to the time domain leads to the exponential decay law. In contemporary dielectric physics the Debye model finds only a little application and to fit the experimental data it is usually replaced by phenomenologically rooted modifications among which the Cole-Cole, Cole-Davidson, Havriliak-Negami and “excess wings” models play dominant role. The first three of them, like the Debye pattern, still depend on a single characteristic time $\tau^{*}$ but involve insertion of fractional powers $0<\ɑlpha,\beta<1$ according to $\chi(i\omega)=(1+(i\omega\tau_{D})^{\alpha})^{-\beta}$. Meanwhile, the “excess wings” model introduces additional characteristic times, e.g. through the ansatz $\chi(i\omega)=(1+(i\omega\tau_{2})^{\alpha})/( 1+(i\omega\tau_{2})^{\alpha}+i\omega\tau_{2})$. All the above mentioned spectral functions, if treated as functions of a complex variable $z$, share a common behaviour – for suitably adjusted, but physically well justified values of parameters, they are analytic in the lower half of the complex plane and map it into the upper halfplane. On first sight this property seems negligible but appears to have important mathematical consequences. Functions which obey it have uniquely determined integral representations given as weighted sums of Debye’s spectral functions (in mathematics equivalent to the so-called Stieltjes transforms of such weight functions) and if transformed to the time domain and taken for $t>0$ are completely monotone, i.e. representable as Laplace transforms (exponential decay law) of nonnegative locally integrable functions. This suggests that widely accepted models of non-Debye dielectric relaxation phenomena may be obtained through summing up elementary Debye relaxations with different, continuously distributed characteristic times. In the talk we are going to provide arguments if this statement should be treated as a mathematical artefact or physically based conjecture.
        [1] R. Garrappa, F. Mainardi, and G. Maione, Frac. Calc. and Appl. Anal. 19, 1105 (2016) [2] K. Górska, A. Horzela, Ł. Bratek, G. Dattoli, and K. A. Penson, J. Phys. A: Math. Theor. 51, 135202 (2018).

        Speaker: Andrzej Horzela (Institute of Nuclear Physics IFJ PAN)
      • 25
        The causality-composition law in the non-Debye relaxations models

        The standard approach to represent the experimentally measured data depending on some continuous parameter is to draw them as a curve, i.e. as a continuous function which fits the experimental points and hopefully follows some theoretical explanation. The most typical illustration of such procedure is a graphical representation of the time evolution of some physically relevant quantity. However, any time evolution pattern must satisfy a crucially important condition: its initial point may be chosen arbitrarily but has to be earlier than the final point. Thus, we can say that any result must not precede its cause and the fitted curve is to satisfy the causality law. This requirement leads also to the composition law. Namely if the system evolves from t0 to t such that t0 < t and if we choose an intermediate instant of time tint, t0 ≤ tint ≤ t, then the composition of evolution in the intervals (t0, tint) and (tint, t) must give the same result as the evolution in the interval (t0, t). This basic property, easily seen for the Debye, i.e. exponential law, is not so evident for non-Debye relaxation phenomena. We show explicitly how it is reakized in two non-Debye relaxation patterns widely used in dielectric physics, namely the Cole-Cole model and the Kohlraush-Williams-Watts (stretched exponential) model observed in the photoluminescence.

        [1] K. Górska, A. Horzela, and A. Lattanzi, Phys. Lett. A 383 (2019) 1716.
        [2] K. Górska, A. Lattanzi, and G. Dattoli, Fract. Calcul. Appl. Anal. 21 (2018) 220.
        [3] G. Dattoli, K. Górska, A. Horzela, S. Liccardi, and R. M. Pidatella, Eur. Phys. J. 226 (2017) 3427.
        [4] K. Górska, A. Horzela, K. A. Penson, G. Dattoli, and G. H. E. Duchamp, Fract. Calcul. Appl. Anal. 20 (2017) 260.
        [5] G. Dattoli, K. Górska, A. Horzela, and K. A. Penson, Phys. Lett. A 378 (2014) 2201.

        Speaker: Katarzyna Gorska (Institute of Nuclear Physics, PAS)
    • Invited Talk
      • 26
        The influence of non-stoichiometry on the order and dynamics of oxides studied by inelastic neutron scattering

        Oxygen ionic conductors are materials of fundamental interest for the development of ambient temperature working devices for energy conversion, such as solid oxide fuel cells (SOFC)
        Inelastic and neutron scattering experiments, coupled with ab-initio molecular dynamics simulations (AIMD), give the unique chance to unveil the presence of specific low-energy modes favoring diffusion events and so explaining the unusual high mobility down to moderate temperatures.

        Experiments and AIMD on Nd2NiO4 systems [1-2] allowed to depict the on-site motion of the diffusive species and understand the impact of oxygen over-stoichiometry on the lattice dynamics of the Nd2NiO4 framework. A recent analysis on a single crystal allowed us to go beyond and verify that this partially disordered non-stoichiometric system show both correlated and uncorrelated dynamics, quite surprising for a crystalline compound.

        Speaker: Andrea Piovano (Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France)
    • 10:40 AM
      Coffee Break
    • Keynote talk
      • 27
        Near-field THz nanoscopy with novel accelerator-based photon sources

        This talk advertises scattering-type scanning near-field infrared nanospectroscopy (s-SNIM) in the spectral range of 75 to 1.2 THz [1,2], as provided by the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Germany. By combining s-SNIM with FELBE, we demonstrate a -independent optical resolution of ~10 nm only, by exploring structured Au samples, Graphene-nanotransistors, meta-materials [3,4], and local-scale ferroic phase-transitions [5 - 7] down to LHe temperatures [8]. Moreover, also the non-linear optical responses at IR wavelengths can be explored as recently demonstrated when inspecting highly-doped GaAs/InGaAs core/shell nanowires [9]. Our THz-s-SNIM was also integrated into a THz pump-probe setup for the local analysis of excited states in structured SiGe samples. We developed a sophisticated demodulation technique that extracts pump-induced signals with a superior signal-to-noise ratio [10]. In addition, HZDR recently extended the available wave¬length ranges down to the 100 GHz radiation, employing the novel super-radiant TELBE light source [11,12]. We adapted our s-SNIM to that novel TELBE photon source as well, achieving an equally high spatial resolution as with FELBE. This allows now to bridge the famous THz-gap in order to explore novel quantum phenomena of magnons, spins, and phonon polaritons.
        [1] F. Kuschewski et al., Appl. Phys. Lett. 108, 113102 (2016).
        [2] S.C. Kehr et al., Synch. Rad. News 30, 31 (2017).
        [3] S.C. Kehr et al., ACS Photonics 3, 20 (2016).
        [4] M. Fehrenbacher et al., Nano Lett. 15, 1057 (2015).
        [5] J. Döring et al., J. Appl. Phys. 120, 084103 (2016).
        [6] J. Döring, LME, et al., Appl. Phys. Lett. 105 , 053109 (2014).
        [7] A. Butykai, LME, et al., Sci. Rep. 7, 44663 (2017).
        [8] D. Lang, LME, et al., Rev. Sci. Instrum. 89, 033702 (2018).
        [9] D. Lang, LME, et al., Nanotechnology 30, 084003 (2019).
        [10] F. Kuschewski, LME, et al., Sci. Rep. 5, 12582 (2015).
        [11] B. Green et al., Sci. Rep. 6, 22256 (2016).
        [12] S. Kovalev et al., Struct. Dyn. 4, 024301 (2017).

        Speaker: Lukas M. Eng (Institute of Applied Physics, School of Science, TU Dresden, 01062 Dresden, Germany)
    • Morning Session 2: Chair: Winfried Petry (Technische Universität Muenchen (Germany)
      • 28
        A novel beamline for advanced photoelectron spectroscopy with narrowband extreme ultraviolet high harmonics at variable high repetition rate

        Spectroscopy in the femtosecond time domain can both reveal fundamental insight in the properties of
        materials and provide relevant experimental tests for functional systems. The quest for sources of
        ultrashort photon pulses (~100 fs) in the Extreme Ultraviolet (EUV) region operating with an adjustable
        repetition rate up to the MHz range has led, in this last years, to the development of high harmonic
        generation (HHG) coherent sources based on table-top lasers. In particular, a comprehensive
        characterization of the photoelectron final state in ordered solids requires measurement, with a subpicosecond time resolution, of energy, momentum and spin-polarization of the photo-emitted current,
        with an energy and a momentum resolution comparable to those achieved using advanced synchrotron
        radiation sources.
        We have built and characterized a versatile twin-beamline for advanced photoemission experiments
        based on a table-top laser HHG source operating in the EUV range beyond 200 kHz repetition rate. The
        beamline is able to provide 1012 photons/sec in the range 15-35 eV, and 109 photons/sec up to 75 eV, with
        variable repetition rate, allowing one to measure shallow core level photoemission spectra in combination
        with valence band ones.
        Experiments on metal and topological insulator have been performed to test the capabilities of the
        beamline, showing a pulse duration shorter than 100 fs and an energy resolution lower than 35 meV.
        The possibility to choose the optimal repetition rate for a given experiment (up to at least 200 kHz, or
        lower) makes it possible to explore a wide excitation-fluence range in pump-probe experiments,
        minimizing sample heating when relevant.
        The twin-branch beamline operates as a users facility. It represents a unique instrument for dynamical
        "all resolved photoemission experiments" to study excited states and transient electronic and magnetic
        configurations at surfaces, nanostructures and solids, with the possibility of covering the full Brillouin zone
        of complex materials.

        Speaker: Riccardo Cucini (C.N.R. - I.O.M)
    • Tour to Legnaro (INFN Laboratory)
    • 1:15 PM
      Lunch in Legnaro
    • Legnaro INFN Laboratory visit
    • Keynote talk
      • 29
        Structural phase transitions from first-principles calculations

        Describing atomic vibrations from first-principles accurately is of paramount importance to
        understand the thermodynamic and transport properties of solids, especially to understand
        structural phase transitions. Phonon dispersions are routinely calculated within the harmonic
        approximation, and transport properties can be studied by estimating the electron-phonon
        and phonon-phonon interactions within perturbation theory. Nevertheless, whenever the
        amplitude of the atomic displacements largely exceeds the range in which the harmonic
        potential is valid, the harmonic approximation completely fails without allowing a
        perturbative expansion. This clearly hinders any ab initio calculation of structural phase
        transitions in these situations
        The stochastic self-consistent harmonic approximation (SSCHA) that we have developed
        [1,2,3,4] offers an efficient method to calculate vibrational properties of solids even when the
        harmonic approximation completely collapses. The method is variational and takes into
        account quantum and thermal effects rigorously. With our recent developments on the
        SSCHA method [3], we show how phonon frequencies should be defined from the second
        derivative of the free energy, which allows calculating the transition temperature of structural
        second-order phase transitions. Moreover, the new developments [3] allow calculating thirdorder anharmonic force-constants, which determine thermal properties, beyond the
        perturbative limit.
        In this lecture we will present the method and several applications of it in superconducting
        hydrides, charge-density-wave systems, and thermoelectric materials.
        [1] I. Errea, M. Calandra, and F. Mauri, Phys. Rev. Lett. 111 (2013) 177002.
        [2] I. Errea, M. Calandra, and F. Mauri, Phys. Rev. B 89 (2014) 064302.
        [3] R. Bianco, I. Errea, L. Paulatto, M. Calandra, and F. Mauri, Phys. Rev. B 96 (2017)
        [4] L. Monacelli, I. Errea, M. Calandra, and F. Mauri, Phys. Rev. B 98 (2018) 024106.

        Speaker: Ion Errea (University of the Basque Country)
    • Morning Session 1: Chair: Andrzej Horzela (Institute of Nuclear Physics, Polish Academy of Sciences, Cracow (Poland))
      • 30
        Vibrational properties of closo – borane anions in superionic conductors

        Metal closo-borate compounds have attracted recent attention as superionic lithium or sodium conductors. In Na2B12H12 or Li2B12H12 the superionic phases are related to the temperature induced phase transitions [1]. Modification of the crystal structure or ion substitution provide the means of tuning their cation conductivity. Spectroscopic fingerprint of internal closo anion (B12H122-) vibrations provides unique opportunity to study influence of such modification in the crystal properties. Dynamical fingerprint of anion vibrations is related to the nature of cation – anion interactions.
        We report on theoretical calculations of the change of IR and Raman modes of B12H12 structure upon deformation along the high symmetry axes as well as interaction of such anion with model configuration of cations. These anions are aromatic structures and even smallest deformations are related to changes in B – H stretching frequencies of entire structure. Deformation is related to change of the electronic structure that extends over whole anion. Our systematic studies of anion dynamical properties are confronted with experimental evidence of Raman modes and cation conductivity.

        Speaker: Zbigniew Łodziana (Institute of Nuclear Physics PAS)
      • 31
        Adsorption of oxygen species on the SnO2 (110) defective surface: a DFT investigation

        Adsorption of oxygen species on the SnO2 (110) defective surface: a DFT investigation

        Speaker: Soufiane Krik (Department of Physics and Earth Sciences, University of Ferrara)
      • 32
        Non-Debye vs Debye Dielectric Relaxation: How does memory effect arise?

        The Debye model presents an essential and elegant description for the relaxation phenomena based on statistical mechanics. However, this model describes systems characterized by a single relaxation time as perfect liquids and crystals, quite far for the complexity which affects almost all amorphous and glassy materials.
        The Debye model has been used as a starting point for other dielectric relaxation theories, named non-Debye (or anomalous) relaxation models, as for example the Havriliak-Negami relaxation model.

        All these models show a power law decay behaviour for the response function as experimentally proved. A useful and powerful mathematical tool for investigating this behaviour is the fractional calculus.

        The present study deals with a novel approach involving a fractional generalization for the time and frequency variables.
        This approach allows us to generalize the Debye’s idea to more complex systems addressing the problem from another point of view complementary to the well-known one ruled by fractional calculus.
        In particular this method examines the time-domain response function defined in terms of a Gamma distribution. The complete monotonicity of the pulse response function follows directly from our investigations.
        Moreover, this method encourages the emergence of the fading memory effects as an intrinsic feature of these complex systems due to the presence of the Gamma distribution.

        Speaker: Ambra Lattanzi (IFJ-PAN)
      • 33
        Efficient calculation of anisotropic Fermi surface problems through Helmholtz Fermi Surface Harmonics (HFSH)

        In metals, the details of the Fermi surface and the magnitude of the matrix elements connecting different points defined on it determine most of their transport properties, which are limited by the electron-phonon coupling and the scattering by impurities. Typically, the calculation of an anisotropic physical property defined on the Fermi surface, say in an impurity or Boltzmann transport problem, requires the consideration of several thousands of points on the surface. In contrast, the Helmholtz Fermi Surface Harmonics (HFSH) technique allows us to accurately treat these problems considering few elements of the HFSH set.

        Here we introduce the recent developments we have implemented in this direction, including the symmetry treatment and the derived selection rules, and we show a representative benchmarking list of examples illustrating the potential of this method.

        Speaker: Jon Lafuente-Bartolome (University of the Basque Country (UPV/EHU))
      • 34
        Ensamble sampling for lattice dynamics

        Computational investigation of anharmonic and temperature-dependent aspects of lattice dynamics requires, among other things, replication of the conditions of thermal equilibrium. This requirement is very challenging when performing quantum mechanical calculations. Typically, it involves large number of atoms and long simulation times needed to approximate thermodynamical limit conditions. This is usually achieved by running a long molecular-dynamics calculation on the system, to thermalize all degrees of freedom, and selecting well-separated (independent) configurations from the obtained trajectory. While this approach provides good sampling of the configuration space of the system it is computationally very expensive and exceptionally wasteful. To obtain independent samples the selected times in the trajectory must be separated by multiple time steps - often tenths or hundreds. Thus, we are throwing away a large amount of computational time, often above 80%, to obtain good sampling of the probability distribution in the configuration space. Furthermore, in the case of lattice-dynamical calculations, we are using only the positions from the trajectory - since we have usually no use for the velocity information. Together, this makes the described procedure limited to fairly small systems.
        In this work we present an alternative scheme for creating a representation of the probability distribution in the configuration space, which aims to faithfully reproduce densities generated by the molecular dynamics, while being much more effective in terms of computational time. This approach uses well-known techniques of probability distribution modelling, and apply knowledge of the behaviour of the system in thermodynamic equilibrium to obtain low sample rejection rate in the procedure. This method, coupled with the effective-potential modelling of the interatomic forces provides a promising path to tackle problems of anharmonic and temperature-dependent lattice dynamics even in systems with large and complicated unit cells.

        Speaker: Paweł Jochym (Department of Computational Materials Science, Institute of Nuclear Physics, PAN)
    • Invited Talk
      • 35
        Polycrystalline time-of-flight inelastic neutron scattering beyond the density of states

        Conventionally, experimental phonon dispersions are determined by inelastic neutron scattering on triple-axis spectrometers or by inelastic X-ray scattering, in both cases requiring single crystalline samples. When only polycrystals are available, the energy-dependent density of states (DOS) can be measured as an alternative.

        Here I will make the point that the (|Q|,E)-dependent spectral density, which is the primary quantity measured in coherent time-of-flight scattering on polycrystals, has a much greater information content than the DOS, to which it is customarily reduced, and that this information can be accessed by modelling the scattering signal. I will present applications of this technique to different systems and specifically show how the efficiency of the method makes it possible to perform temperature-dependent measurements with fine resolution, such as the behaviour of the phonon frequencies around the α-γ transition in elemental iron.

        Fig. 1. Time-of-flight spectra of polycrystalline Nickel: measured (left) and simulated (right)

        Speaker: Michael Leitner (Technische Universität München)
    • 10:40 AM
      Coffee Break
    • Invited Talk
      • 36
        Rubidium at Extreme Conditions

        Transformations of alkali metals at high pressures is one of the hot topics of modern condensed matter physics. Exotic crystalline structures with very large and complex unit cells, unusual melting lines showing maxima and minima, pressure induced metal to non-metal transitions are some examples of this fascinating scenario. I will describe recent X-ray diffraction (XRD), Raman spectroscopy and Inelastic X-ray Scattering (IXS) studies on liquid and solid Rubidium at extreme pressures, up to several tens of GPa. XRD and IXS data in diamond anvil cells (DACs) consistently show a liquid−liquid transformation from a simple metallic liquid to a complex one, occurring at 6.5-8.5 GPa, which is slightly above the first maximum of the T−P melting line [1,2]. This transformation is traced back to the density-induced hybridization of highest electronic orbitals (s-d transition) leading to the accumulation of valence electrons between Rb atoms and to the formation of interstitial atomic shells, a behavior that Rb shares with Cs and is likely to be common to all alkali metals. Similarly, in the solid state, compressed alkali metals up to tens of GPa exhibit complex low-symmetry modifications, due to the density-driven transition of the valence electrons from the s state to states of higher angular momentum. We conducted challenging Raman spectroscopy measurements in DACs and ab initio computer simulations on the optical phonons of the low symmetry, high pressure crystalline phases of Rb up to 100 GPa [3]. The relative (relative to the normal condition value) density behavior of Raman frequencies of Rb is compared to that of Na and Li, once the frequencies of the two light alkali elements have been properly rescaled by their masses. Importantly, while the rescaled density behaviors of Na and Li agree with each other, Rb significantly differs, which highlights the different nature of the valence electron transition being of the s-d and of the s-p type in heavy and light alkali metals, respectively, a result that calls for further similar investigations of K and Cs. Ab initio simulations help the data analysis and show the evolution of the electronic, structural and dynamic properties in Rubidium extending to conditions still difficult to reach experimentally.

        [1] F. A. Gorelli, S. De Panfilis, T. Bryk, L. Ulivi, G. Garbarino, P. Parisiades, M. Santoro, J. Phys. Chem. Lett. 9, 2909 (2918).
        [2] T. Bryk, S. De Panfilis, F. A Gorelli, E. Gregoryanz, M. Krisch, G. Ruocco, M. Santoro, T. Scopigno, and A. P. Seitsonen, Phys. Rev. Lett. 111, 077801 (2013).
        [3] M. Santoro, D. Colognesi, B. Monserrat, E. Gregoryanz, L. Ulivi, and F. A. Gorelli, Phys. Rev. B 98, 104107 (2018).

        Speaker: Mario Santoro (INO-CNR and LENS)
    • Morning Session 2: Chair: Renato Torre (European Lab. for Non-Linear Spectroscopy (LENS) and University of Firenze, Firenze (Italy)
      • 37
        Impact of high-pressure evolution of elementary distortions on the phase-transition of RFeO_3

        Rare-earth orthoferrites (RFeO3) have been intensively studied in last years, as they exhibit a variety of interesting physical properties, with a large number of works having addressed the underlying microscopic mechanisms [1]. The rare-earth size drives the cooperative rotations of the FeO6 octahedra, which is known to linearly scale with the octahedra tilt angles [1]. Their physics has been studied with hydrostatic pressure as external parameter. Though empirical rules regarding the pressure dependence of octahedral tilts and rare-earth displacements in 3:3 perovskites have been proposed [2], a systematic and detailed experimental study of the pressure evolution of the lattice distortions of a representative set of RFeO3 is still missing. Moreover, contradictory theoretical results have been discussed in literature, such as the prediction that the octahedral tilts and rare-earth displacements should decrease with pressure, via their trilinear coupling [2]. This decrease should yield a structural phase transition into a higher-symmetric structure at some critical pressure PC, which, in fact, is not the case of RFeO3, presenting a pressure-driven isostructural transition [3].
        Our work reports on the evolution of the octahedral tilts and mean Fe-O bond lengths of RFeO3 (R = Nd, Sm, Eu, Gd, Tb and Dy) with applied hydrostatic pressure by Raman scattering and synchrotron XRD up to 55 GPa. We have found out that the octahedra tilts decreases with pressure for R = Nd-Sm, whereas it increases for R = Tb-Lu, affecting the displacement of the rare-earths due to trilinear coupling, and compression rate of the FeO6 octahedra [3]. EuFeO3 stands at the borderline, with nearly pressure-independent tilt angles. The surprising crossover between the two opposite pressure behaviors is discussed in relation with the general rules proposed from different theoretical approaches. The similarity of the pressure-induced isostructural insulator-to-metal phase transition, observed in the whole series, point out that the tilts play a minor role in its driving mechanisms. A clear relationship between octahedral compressibility and critical pressure is ascertained with respect to a critical volume of the FeO6 octahedra.

        [1] E. Bousquet and A. Cano, J. Phys.: Cond. Matt. 28, 123001 (2016)
        [2] H. J. Xiang, J. Íñiguez, J. Kreisel and L. Bellaiche, Phys. Rev. B 96, 054102 (2017)
        [3] R. Vilarinho, P. Bouvier, M. Guennou, I. Peral, et al., Phys. Rev. B 99, 064109 (2019)

        Speaker: Rui Vilarinho (IFIMUP, Departament of Physics and Astronomy, Faculty of Sciences, University of Porto )
      • 38
        Investigation of high pressure phase transition by means of infrared spectroscopy in the Cairo frustrated pentagonal magnet Bi2Fe4O9

        Bi2Fe4O9 is a common by-product in the synthesis of the multiferroic compound BiFeO3 and has been claimed itself to display multiferroic properties [1]. The lattice formed by the two different sites of four iron Fe3+ magnetic atoms is quite remarkable as it materializes the first analogue of a magnetic pentagonal lattice [2]. For its peculiar lattice geometry it has attracted interest in the field of geometrical frustration. At room temperature and atmospheric pressure, the crystal structure is orthorhombic within the Pbam space-group and the compounds undergoes a magnetic phase transition at 238 K from a paramagnetic state toward a non collinear magnetic state characterized by a propagation vector k = (1/2,1/2,1/2) and a large degree of frustration (θp/TN ~ 7) [2]. Recently it has been shown that Bi2Fe4O9 undergoes a structural transition under pressure at 6-8 GPa toward the maximal non-isomorphic subgroup Pbnm, with c’ = 2c. The driving force of the phase transition is the displacement of the O1 oxygen atom from fully constrained Wyckoff position 2b to a less-constrained 4c one [3]. Previous studies have reported the investigation of dynamical properties by mean of Raman spectroscopy both at ambient condition and at high pressure in a diamond anvil cell [3,4]. However, the vibrational modes involving O1 oxygen atoms are not Raman active but infrared active.
        We will report the first polarized infrared spectroscopy measurement of Bi2Fe4O9 performed in a DAC from 1 to 20 GPa in the far-infrared range [60-800 cm-1] and at low temperature. The measurements have been performed at the AILES beamline of synchrotron SOLEIL exploiting the high-pressure/low-temperature set-up [5] coupled with the high brilliance of the radiation source in a wide spectral range on a very thin sample (~50 µm) placed between diamonds with culets of 500 µm diameter. From our high quality spectra, we are able to identify the B3u and B2u modes within the (ab)-plane. Interestingly, while all phonon frequencies increase with pressure, the phonon mode around 200 cm-1 undergoes an anomalous softening with increasing pressure. In order to assign the phonon modes and reveal the microscopic mechanism of the high-pressure transition we also have performed DFT calculation at different pressures. The calculation mostly accounts for the measured phonon modes allowing the assignation of atomic motions.

        [1] A. K. Singh, et al., Applied Physics Letters 92, 132910 (2008).
        [2] E. Ressouche, et al., Review Letters 103, (2009).
        [3] A. Friedrich, et al., Journal of Physics: Condensed Matter 24, 145401 (2012).
        [4] M. N. Iliev, et al., Physical Review B 81, (2010).
        [5] A. Voute, et al., Vibrational Spectroscopy 86, 17 (2016).

        Speaker: Marine Verseils (Ligne AILES - Synchrotron SOLEIL)
      • 39
        Advances on the modelling of blood flows and pressures in humans through a new multiscale mathematical model

        Many biophysical factors affect human circulation, so that a satisfactory understanding of its behavior is challenging [1]. Moreover, congenital vascular disease is the leading cause of pediatric death, and it is proven that physiological parameters such as cardiac output, cerebral blood flow, and arterial stiffness are related to age [2]. For these reasons, the assessment of cardiovascular structure and function is recognized as a main topic in the history of scientific research [3]. We developed a mathematical model to simulate cerebral and extracerebral flows and pressures in humans. The model is composed of an anatomically informed 1-D arterial network [4] [5], and two 0-D networks of the cerebral circulation and brain drainage, respectively [6] [7]. It takes into account the pulse-wave transmission properties of the 78 main arteries and the main hydraulic and autoregulation mechanisms ensuring blood supply and drainage to the brain. Proper pressure outputs from the arterial 1-D model are used as input to the 0-D models, together with the contribution to venous pressure due to breathing that simulates the drainage effect of the thoracic pump. The model is able to evaluate the effects of reduced/elevated carbon dioxide in the blood (hypo/hypercapnia) [8], and to compare adult and pediatric circulation through a straightforward calibration of the parameters. Proper MRI and ultrasound datasets were used to extract information about blood rheology (e.g. blood velocity and flow), and vessel status (hydraulic resistance and capacitance, inner pressure and cross section area). The model has the potential to predict important clinical parameters before and after physiological and pathological changes with focus on head and neck circulation, such as posture changes, vessel occlusions, venous thrombosis, and congenital diseases.

        [1] Fung. Biomechanics. Circulation, edited by Springer-Verlag (New York, USA, 1997)
        [2] C. Wu, J. Am. Heart Assoc. 5(1), e002657 (2016)
        [3] K.P. George, Eur. J. Appl. Physiol. 118(6), 1079 (2018)
        [4] M. Majka, Math. Biosci. 286, 16 (2017)
        [5] M. Majka, Phys. Rev. E. 95(3-1), 032414 (2017)
        [6] G. Gadda, Am. J. Physiol. Heart Circ. Physiol. 308(3), H217 (2015)
        [7] G. Gadda, AJNR Am. J. Neuroradiol. 37(11), 2100 (2016)
        [8] G. Gadda, Eur. J. Appl. Physiol. 118(11), 2443 (2018).

        Speaker: Giacomo Gadda (Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara)
    • 12:30 PM
    • Afternoon Session 1: Chair: Alain Sacuto (Université Paris Diderot, Paris, (France))
      • 40
        Sub-THz Raman response and critical dynamics in BaTiO3

        Sub-THz Raman response and critical dynamics in BaTiO3 (talk)
        Marc D. Fontana1,2*, Ninel Kokanyan1,2, and Thomas H. Kauffmann1,2
        1Université de Lorraine, CentraleSupélec, LMOPS, F-57000 Metz, France
        2Laboratoire Matériaux Optiques, Photonique et Systèmes, CentraleSupélec, Université Paris-Saclay, 57070, Metz, France
        BaTiO3 (BTO) is considered as a textbook material for the description of structural phase transitions (SPT) and the appearance of ferroelectricity. On cooling it undergoes successive cubic-tetragonal-orthorhombic-rhombohedral (C-T-O-R) phase transitions [1]. Various concepts such as soft phonon, central peak, relaxational mode, hard phonon are invoked to describe the dynamics of the lattice, the structural changes or the occurrence of ferroelectric state in this material [2,3,4,5]. The displacive or order-disorder (OD) character of the paraelectric-ferroelectric transition is long-standing object of controversies [4,6]. It is now admitted that both mechanisms co-exist [7,8]. It is to be underlined that up to now the simultaneous detection of both processes by the same technique was not so far reported. The possibility of existence of two critical degrees of freedom was only drawn by ab-initio calculations [9], or was indirectly derived from the discrepancy in dielectric permittivity between direct data and calculations via LST relationship [6,7]. Raman spectroscopy was widely used for investigate lattice dynamics and phase transition in BTO, but the very high damping of the soft phonon [3,10] impedes to extract the additional OD feature which should be located at lower frequency. Here we report new Raman spectra recorded as function of temperature in the tetragonal phase, using ultra low-frequency (ULF) set-up. This tool provides the measurement of Raman shift down to 5 cm-1 with respect of the Rayleigh line, providing therefore the detection of vibrational or relaxational modes centered around 200 GHz. Within the contribution we firstly discuss the differences and similarities in the various concepts used to describe lattice dynamics with link with SPT. Then we present new Raman data in BTO and highlight the occurrence of the additional peak lying at frequency lower than the soft phonon. The intensity and shape of this peak are strongly dependent on temperature. This feature is attributed to a local mode, related to Ti- off centering with a characteristic relaxation frequency showing a slowing down on approaching the T-C, and the T-O SPT as well.
        [1] F.Jona and G.Shirane, Ferroelectric crystals, (MacMillan, New York), 1962
        [2] K.A Muller, Y.Luspin, J.L. Servoin, and F.Gervais, J.Physique 43, L537 (1982)
        [3] H. Vogt, J.A. Sanjurjo and G. Rossbroich, Phys. Rev. B 26, 5904 (1982)
        [4] J. P. Sokoloff, L. L. Chase and D. Rytz, Phys. Rev. B 38, 597 (1988).
        [5] M.D.Fontana, K.Laabidi and B.Jannot, J.Phys. Condens. Matter, 6, 8923 (1994)
        [6] K. Laabidi, M. D. Fontana, M. Maglione, B. Jannot and K. A. Muller, Euro. Phys. Lett. 26, 309 (1994).
        [7] J. Hlinka, T. Ostapchuk D. Nuzhnyy, J. Petzelt, , P. Kuzel, C. Kadlec, P. Vanek, I. Ponomareva and L. Bellaiche, Phys. Rev. Lett. 101, 167402 (2008).
        [8] H.Y.Deng, EPL 100, 270001 (2012).
        [9] W. Zhong, D. Vanderbilt and K.M Rabe, Phys Rev B 52, 6301 (1995).
        [10] G.Burns and F.H Dacol, Phys. Rev. B 18, 5750 (1978).

        Speaker: Marc Fontana (Univ Lorraine, Metz, France)
      • 41
        Narrow Optical Gap Ferroelectric Bi2ZnTiO6 Thin Films Deposited by RF Sputtering

        This work reports the deposition of single phase Bi2ZnTiO6 thin films onto Pt/Si-based substrates using rf-sputtering method and the respective structural, morphological, optical and local ferroelectric characterization. The thin film grows in the polycrystalline form with tetragonal P4mm symmetry identified by X-ray diffraction. The lack of spatial inversion centre was confirmed by the second harmonic generation. A narrow indirect optical gap of 1.48 eV was measured using optical diffuse reflectance. The ferroelectric domain reversal was further demonstrated through piezo-response force microscopy. This work demonstrates a practical method to fabricate the BZT perovskite phase with outstanding optical and ferroelectric properties, without recurring to high pressure and temperature conditions necessary to synthetize the bulk form.
        [1] J. Mater. Chem. A 2019 doi: 10.1039/C8TA09425J

        Speaker: Fábio Figueiras (IFIMUP & Physics and Astronomy Department, Sciences Faculty, Porto University)
      • 42
        Electron localizations in alloy exhibiting nanotwinning

        Ni$_{2}$MnGa is a multiferroic ferromagnetic shape memory alloy in which a large spontaneous deformation up to 12% has been observed after application of an external magnetic field [1]. The key to material functionalities is the ferroelastic microstructure of martensite with deep hierarchical twinning up to nanoscale [2]. However, the microscopic origin of the martensitic transformation between the high temperature austenitic and low temperature martensitic phases is not fully understood to date as well as exact origin of nanotwining in martensitic phases. In present work we have used first-principles calculations based on density functional theory (DFT) to simulated magneto-optical (MO) Kerr spectra for different phases of Ni$_{2}$MnGa alloy: austenite, nonmodulated martensite without nanotwinning and nanotwined martensite represented by 4O structure [3]. MO spectra provides a valuable insight into the mutual dependence of the electronic structure and magnetic ordering on the structure of the material.

        The work of Himmetoglu et al. [4] suggests that the Hubbard treatment of the on-site Coulomb interaction of d-electrons localized on Mn sites (DFT+U) is required to achieve properly the electronic structure of Ni2MnGa alloy. A comparison of the calculated and measured spectra allowed us to estimate the proper value of Coulomb interaction parameter U, which we found significantly smaller than the value proposed in previous works [4,5]. Using the new parameter U, we obtain a better quantitative agreement with experiment at least in case of elastic constants and lattice parameters in Ni$_{2}$MnGa. Comparison of the newly calculated densities of states covering the electron localization then provides a better insight into the origins of martensitic transformation and nanotwinning.

        [1] M. Acet, Ll. Mañosa, A. Planes, Handb. Magn. Mater. 19, 231 (2011).
        [2] S. Kaufmann et al., New J. of Phys. 13, 053029 (2011).
        [3] M. Zelený, L. Straka, A. Sozinov, O. Heczko, Phys. Rev. B 94, 224108 (2016).
        [4] B. Himmetoglu, V. M. Katukuri, M. Cococcioni, J. Phys. Condens. Matter. 24, 185501 (2012).
        [5] T. Koubský et al., Acta Phys. Pol A 134, 804 (2018).

        Speaker: Martin Zelený (Faculty of Mechanical Engineering, Brno University of Technology)
      • 43
        Molecular dynamics simulations of ferroelectric perovskites (BaTiO3 , BiFeO3) based on the effective Hamiltonian approach

        The theoretical description of ferroelectric perovskite materials at finite temperatures is commonly analyzed using Landau-Ginzburg type phenomenological models, and Monte-Carlo [MC] or molecular dynamics [MD] simulations. The parametrization of the phenomenological potentials originates from experimental data or from first principal calculations [1]. The MC and MD simulations use as bases the zero-temperature energy potentials determined from ab-initio calculations. There are commonly used two main approaches, the effective Hamiltonian method [2] and core-shell atomic-level simulations [3].

        In this work, we address the structural and polar properties, the phase transition sequence of BiFeO3 and BaTiO3 at finite temperatures using molecular dynamic simulations based on the effective Hamiltonian, which was determined from ab-initio calculations, with strain, polarization, and oxygen octahedra tilt degrees of freedom [4]. The ground state energy landscape of the effective Hamiltonian is parametrized up to high orders at degrees of freedom. Such parametrization can precisely characterize the ordered phase and domain wall properties. To characterize the ferroelectric phase transitions we perform the simulations for various temperatures and compare them with outcomes of the core-shell approach [5].

        [1] F. Xue, Y. Gu, L.Liang, Y. Wang, and L. Q. Chen, Phys. Rev. B 90, 220101 (2014).
        [2] Vanderbilt D. First-principles based modelling of ferroelectrics. Curr.. Opin. Solid State Mater. Sci. 2:701–5. (1997)
        [3] M. Sepliarsky, A. Asthagiri, S.R. Phillpot, M.G. Stachiotti, R.L. Migoni, Curr. Opin. Solid State Mater. Sci. 9 107. (2005)
        [4] P. Marton, A. Klic, M. Pasciak, and J. Hlinka: Phys. Rev. B 96, 174110 (2017)
        [5] Graf, M., Sepliarsky, M., Machado, R., Stachiotti, M.G.: Solid State Communications, 218, pp. 10-13 (2015)

        Speaker: Antonín Klíč
      • 44
        Tetragonal Ferroelectric Phase of GdMnO3 Epitaxial Thin Film Grown onto SrTiO3 (001)

        High quality GdMnO3 thin films were deposited on SrTiO3 (001)-oriented substrates by RF magnetron sputtering. The structure, microstructure and polar properties were investigated in detail. The films grown up to a 35 nm thickness exhibit an epitaxial non-relaxed tetragonal symmetry, where the basal lattice parameters are imposed by the cubic symmetry of the substrate, contrarily to the expected orthorhombic one. In Addition, the slower growth rate imposed by the RF-sputtering method, in comparison to other synthesis processes, can contribute to largely extend the thickness threshold for which the GdMnO3 phase can yield epitaxially grown tetragonal films. Furthermore, a noteworthy variation of electric polarization was observed around 31 K that is apparently a consequence of the significant structural distortions occurring below that temperature. The stabilization of an improper ferroelectric phase occurring at low temperatures points to a substantial differentiation concerning the GdMnO3 in orthorhombic form.

      • 45
        Unravelling the Magnetoelectric Coupling Mechanisms in TbMnO_3 through Fe3+ substitution

        Multiferroics, such as orthorhombic rare-earth manganites, where both magnetic and ferroelectric orders coexist and are coupled to one another, have attracted great interest. The simultaneity of magnetic and ferroelectric phases gives rise to important effects associated with the cross correlation between order parameters and external fields. A remarkable consequence is that the elementary excitations are not purely magnetic nor polar. Spin waves are mingled with the electric polarization related optical lattice modes, giving rise to the so-called electromagnons, whose spectra provide invaluable information on how magnetism couples to the electric polarization. Once the driving mechanisms are well understood, it is of great importance to aim at enhancing their coupling, the so-called magnetoelectric coupling, which is highly desired for advanced technological applications.
        Because $TbMnO_3$ has been the subject of intensive research in this field, it is the ideal case-study compound. In this material, an incommensurate sinusoidal collinear order of the $Mn$ spins occurs at $T_N = 41 K$, wherein the $Mn$ spins lie in the $bc$-plane ($Pbnm$ setting). Below $T_{lock}$ = 28 K, a magnetic transition occurs into a commensurate cycloidal spin order with $Mn$ spins lying in the $bc$-plane, compatible with the stabilization of an improper ferroelectric polarization along the $c$-axis [1]. Furthermore, a magnetic field along the $b$-axis rotates the cycloidal spin order into the $ab$-plane, and thus, the electric polarization to the $a$-axis [1]. Previous studies carried out in $TbMnO_3$ ceramics show that the substitution of $Mn^{3+}$ by small amounts of the identically sized $Fe^{3+}$ ion profoundly changes both magnetic and polar structures, altering the magnetoelectric coupling [2]. In fact, for an $Fe^{3+}$ concentration above $5\%$, the multiferroic properties of the $TbMn_{1-x}Fe_xO_3$ solid solution are lost [2]. Nonetheless, as these studies were done in ceramics, anisotropic effects such as the flop of the cycloidal plane with an applied magnetic field could not be ascertained.
        In this work, oriented single crystals of $TbMn_{1-x}Fe_xO_3$ with $x = 0.02$ and $0.04$ were used to study the polar, dielectric and magnetoelectric properties versus temperature and magnetic field along the crystallographic directions. To further understand the effect of $Mn^{3+}$ substitution by $Fe^{3+}$, $THz$ time-domain spectroscopy as a function of temperature and applied magnetic field was performed. The obtained results will be presented emphasizing the effect of temperature and magnetic field on their physical properties for different $Fe^{3+}$ concentrations, highlighting the contrast with previously reported studies on the unsubstituted compound [3, 4].

        [1] T. Kimura et al., Phys. Rev. B, 71(22), 224425 (2005)
        [2] R. Vilarinho et al., JMMM, 439, 167 (2017)
        [3] Y. Takahashi et al., Phys. Rev. B, 101(18), 187201 (2008)
        [4] A. Pimenov et al., Nat. Phys., 2(2), 97 (2006)

        Speaker: André Maia (IFIMUP-IN, Institute of Nanoscience and Nanotechnology, Department of Physics and Astronomy of Faculty of Sciences, University of Porto, Portugal )
    • 3:25 PM
      Coffee Break
    • Afternoon Session 1: Chair: Iñigo Etxebarria (Universidad del País Vasco UPV/EHU, Bilbao (Spain))
      • 46
        Piezoelectric response of K0.5Na0.5NbO3 designed by sintering engineering

        Since the discovery of the piezoelectric properties of lead zirconate-titanate (PZT) solid solution, namely near its morphotropic phase boundary region (MPB), those materials exhibiting piezoelectricity have been largely studied, wherein PZT still stands as a prototype for electromechanical applications. However, lead based materials are poisonous in nature and thus they should be substitute for lead-free materials to assure sustainability. Though lead-based materials have higher piezoelectric response, there are other promising friendly environment compounds, namely KxNa(1-x)NbO3 [1]. For x=0.5 (0.5KNN), the high-temperature cubic symmetry changes to a non-symmetric ferroelectric tetragonal structure at T3=700 K. At T2=465 K it becomes orthorhombic, stabilizing in a rhombohedral symmetry below T1=135 K [2]. Recently, theoretical calculations have predicted piezoelectric response enhancement when T3 become closer to T2. Moreover, it has been suggested that sintering conditions can act significantly on the magnitude of the [T2, T3] interval. To unravel the effect of sintering conditions in 0.5KNN, ceramics were prepared by conventional sintering (CS), spark plasma sintering (SPS), and spark plasma texturing (SPT). XRD data at room conditions revealed that the two latter methods yield 0.08 and 0.16 GPa of internal stresses, respectively. It is worth emphasizing, that the emergence of theses stresses have strong repercussions on the values of the piezoelectric coefficient d33, increasing from 50 to 125 pC.N-1 for SPS and SPT samples, respectively [3].
        In this work, we present a detailed, temperature dependent, lattice dynamic study of 0.5KNN ceramics produced by the three sintering methods referred to above, using Raman spectroscopy. For the three types of sintered samples, we have observed clear critical temperature shifts, and specific different modes behaviors at T1, T2 and T3. To corroborate this outcome, the temperature dependence of the polar and dielectric properties of the CS, SPS and SPT samples was studied using pyroelectric and dielectric techniques. The obtained results are discussed towards disentangling how the sintering methods tailor the piezoelectric response, in order to provide competitive lead-free materials.

        [1] I. Coondoo et al., J. Advanced Dielectrics, 03, 1330002 (2013)
        [2] B. Orayech et al., J. Appl. Cryst., 48, 318-333 (2015)
        [3] R. Pinho et al., paper to be submitted

        Speaker: Mariana Gomes (IFIMUP-IN, Institute of Nanoscience and Nanotechnology, Department of Physics and Astronomy of Faculty of Sciences, University of Porto, Portugal )
      • 47
        Archetypal Soft-Mode Driven Antipolar Phase Transition in Francisite Cu3Bi(SeO3)2O2Cl

        Antiferroelectricity can be seen as being a property similar to antiferromagnetism with electric dipoles instead of spins. It is characterized by a phase transition between a high- and a low-symmetry phase where antiparallel dipoles emerge [1]. In analogy with soft-mode driven ferroelectric transitions (e.g. in PbTiO3), it is then possible to think of an ideal antiferroelectric phase transition driven by an “anti-polar soft-mode”, which is a soft phonon mode related to antiparallel ionic displacements [2]. However, such a phase transition has not been observed yet; instead, classical antiferroelectric transitions are usually of the order-disorder type.

        In this study, we show that francisite (Cu3Bi(SeO3)2O2Cl) undergoes such an anti-polar soft-mode driven phase transition. Francisite is an orthorhombic crystal that has a phase transition from space group Pmmn to Pcmn at 115 K [3]. This phase transition induces a doubling of the unit cell along the c axis, which folds the zone-boundary Z point (0,0,1/2) of the high-symmetry phase onto the Γ point in the antipolar phase [4]. We measured the low-frequency phonon modes in both phases using a combination of Raman spectroscopy, Inelastic X-Ray Scattering (IXS) and Thermal Diffuse Scattering (TDS). IXS and TDS measurements have been performed at the ID 28 beamline of ESRF [5].

        Raman spectra across the phase transition are shown on Fig. 1. and show a clear soft phonon mode visible only in the low-temperature phase. The soft-mode above Tc on the other hand is seen in the IXS spectra and in the TDS intensity. Fig. 2 shows the combination of experimental data with the soft-mode energy squared as a function of temperature. It displays a typical soft-mode behaviour in the vicinity of Tc, with deviations originating from mode coupling with other low lying phonon modes. The slopes of E2 vs. T indicate that the transition is close to tricritical.

        Fig. 1 is the enclosed "Raman_cascade.jpg" file and Fig 2. is "Soft-mode_evolution.jpg"

        Speaker: Cosme Milesi-Brault (Luxembourg Institute of Science and Technology)
      • 48
        Lattice dynamics and Raman spectrum of BaZrO3 single crystals

        BaZrO3 is a perovskite that exhibits the ideal cubic structure with space group Pm-3m from ambient conditions down to 2 K [1]. However, theoretical studies by DFT yield a more complex picture: the cubic phase is predicted to be slightly unstable, with an unstable phonon mode at the R point, which should give rise to an antiferrodistortive (AFD) transition to a low-symmetry phase with octahedral tilts [1]. Furthermore, our recent DFT calculations [2] indicate that the three possible tilted phases resulting from this instability (I4/mcm, Imma, R-3c), are nearly degenerate, and hardly lower in energy than the cubic phase. Experimentally, BaZrO3 exhibits a strong Raman signal whose origin is unclear, since first-order Raman processes are forbidden in the cubic phase by symmetry. It has been tentatively explained by structural distortions at the nanoscale [3], or by 2nd-order Raman scattering.
        In this work, we took advantage of the recent synthesis of good quality BaZrO3 single crystals [4] to perform Raman measurements in a wide range of temperatures (from 4 K to 1200 K) and under hydrostatic pressure (up to 20 GPa). We present here a detailed comparison of the experimental data with DFT computations of the phonon modes both in the cubic and in the three distorted phases. We show that the phonon modes computed in the distorted phases do not match our experimental results, ruling out the scenario of nanoscale structural distortions. Moreover, the high energy Raman phonon modes seem well described by the overtone density of states computed by DFT in the cubic structure and we provide a thorough analysis of possible assignments to second-order processes. The atomic displacements related to these assignments are also discussed.

        Fig. 1. (a) Experimental Raman spectra at low temperature (4K) in different light polarization configuration showing selection rules and (b) overtone density of states in the cubic phase, for each atomic specie, computed by DFT

        [1] Akbarzadeh et al., Phys. Rev. B, 72, 205104 (2005)
        [2] Amoroso et al., Phys. Rev. B, 97, 174108 (2018)
        [3] Chemarin et al., J. Sol. State. Chem., 149, 298 (2000)
        [4] Xin et al., CrystEngComm, 21, 502-512 (2019)

        Speaker: Constance Toulouse (Physics and Material Science Research Unit, University of Luxembourg, )
      • 49
        2D transition metal carbides as flexible anode materials

        MXenes exhibit many outstanding properties and therefore been considered as promising electrode material candidates. Taking 2D transition metal carbides as representatives, we systematically explored several influencing factors, including transition metal species, layer thickness, functional group, and strain on their mechanical properties (e.g., stiffness) and their electrochemical properties (e.g., ionic mobility). Considering potential charge-transfer polarization, we employed a charged electrode model to simulate ionic mobility and found that ionic mobility has a unique dependence on the surface atomic configuration influenced by bond length, valence electron number, functional group, and a strain. Under multiaxial loadings, electrical conductivity, high ionic mobility, low equilibrium voltage with good stability, excellent flexibility, and high theoretical capacity indicate that the bare 2D TMCs have potential to be ideal flexible anode materials, whereas the surface unctionalization degrades the transport mobility and increases the voltage due to bonding between the nonmetals and Li.

        Speaker: Dominik Legut (VSB - Technical University of Ostrava, IT4Innovations, Ostrava, Czech Republic)
    • Visit to the city
    • 8:00 PM
      Social Dinner
    • Keynote talk
      • 50
        Metal oxide heterostructures and hybrid nano composite for chemical sensors

        In the field of advanced sensor technology, metal oxide nanostructures are promising materials due to their high charge carrier mobility, easy fabrication and excellent stability. In particular, most of them exhibit a reversible interaction between their surfaces with the surrounding atmosphere. This interaction may lead to a change of some different properties of the material, such as electrical conductance, capacitance, work function or optical characteristics. The Metal-oxide semiconductor gas sensors are viable alternates for highly sensitive and selective detection of different gases and air pollutants, which provide various advantages such as miniaturization, low cost gas detection, and real-time monitoring. Various strategies have been used to increase the gas response and selectivity, including modulating the sensing temperature, [1] morphological control, [2] catalyst doping/loading, [3] and catalytic filtering of interference gases [4].
        Another effective strategy to enhance the sensor response and selectivity is to construct the heterojunction between two different oxides that enables the control of conductivity at p-p, p-n, and n-n interfaces, and synergistic catalytic effects between different materials. The framework of the SENSOR laboratory is to studying thoroughly the idea, to bring together the properties of two different nanostructure materials into a single sensing platform by using a common, simple, low cost and high yield growth method. Herein, we report on the novel preparation and characterization of different hetrostructures morphologies such as NiO/ZnO [5] branched 1D-1D nano-heterostructures and NiO/SnO2, CuO/ZnO Core-shell, and SnO2/GO. Several growth techniques has been used for the growth of different heterostructures: vapour phase evaporation and condensation [5], thermal oxidation of a metal film [6], and hydrothermal synthesis and Atomic layer deposition technique. The surface morphology of the nanostructures was investigated by using scanning electron microscopy (SEM) while, for structural characterization GI-XRD, the transmission electron microscopy (TEM), and XPS, Raman spectroscopy, UV-Vis spectroscopy. Figure 1 shows the SEM images of NiO/ZnO, NiO/SnO2, CuO/ZnO, SnO2/GO hetrostructures fabricated on alumina substrate. Finally, heterostructure based conductometric gas sensing devices have been fabricated and tested towards different gases spices such as (NO2, H2, CO, VOC’s) and their performance have been compared with the host materials.
        [1] E. Comini et. al., Sensors Actuators B Chem. 179, 3 (2013).
        [2] Y.-F. Sun et. al., Sensors (Basel). 12, 2610 (2012).
        [3] L. Wang et. al., Mater. Sci. Eng. C 32, 2079 (2012).
        [4] S.-Y. Jeong et. al., J. Mater. Chem. A 5, 1446 (2017).
        [5] Kaur, N, Comini, E, et al. Sens Actuators B Chem, 2018, 262.
        [6] Zappa, D, Comini, E, et al. Sens Actuators B Chem, 2013, 182.

        Speaker: Elisabetta Comini
    • Morning Session 1: Chair: Cesare Malagù (University of Ferrara (Italy))
      • 51
        Bi2O3 and ZnO nanowires growth using Vapor–Liquid–Solid (VLS) process for chemical sensors applications

        Previous and current researches in agreement with industrial needs, aim to reduce the dimensions, reduce the price and enhance the sensing performances. Due to their low-cost production, their possibility of miniaturization and their good sensitivity, metal oxides chemical sensors are attracting particular attention. In this study, we report the preparation of ZnO and other new materials such as Bi2O3 nanowires using the vapor liquid solid (VLS) process for chemical sensing applications. In this context, the detection and monitoring of ozone levels are of critical importance. When its level exceeds specific concentrations, the exposure to this gas becomes dangerous to human health, as it causes headache, burning eyes and breathing problems [1]. On the other hand, profiling the body chemistry by monitoring of volatile organic compounds (VOCs) such as Acetone and Ethanol in the breath opens new possibilities in medical diagnostics and in particular diabetes diagnosis. Therefore, fabrication of one-dimensional metal oxides chemical sensors is considered to be an effective approach to these applications. In this study, Vapor- Liquid- Solid (VLS) process is proposed to produce one-dimensional ZnO and Bi2O3 nanowires.
        ZnO oxides nanowires were optimized using different catalysts to get the best quality of nanowires for Ozone detection. Morphological, structural, optical and electrical properties of 1D ZnO nanostructures will be studied and discussed. Good quality of ZnO NWs obtained using Cu and Au catalysts with high aspect ratio (Fig. 1). The dynamic response of ZnO nanowires under O3 exposure with different concentrations is reported in Fig. 2. ZnO (Au) NWs show highest and best response (645) while ZnO (Cu) NWs have good response (350) to Ozone.
        Bi2O3 have produced using VLS process, characterized and its suitability for chemical application have been proven. High quality of Bi2O3 NWs was produced (Fig. 3). The Au nanoparticles observed on the top of Bi2O3 NWs control the growth and NWs diameters and could enhance the sensing properties. Bi2O3 Sensor was tested under H2, CO, Acetone and Ethanol using different temperatures, and 350 °C was found as the best working temperature. good selectivity for Volatile Organic Compounds (VOCs) was observed (Fig. 4). The response of Bi2O3 to low Acetone concentrations opens possibilities for the utilization of Bi2O3 as a new nanomaterial in medical diagnostics in particularly diabetes diagnostic. Moreover, the effect of relative humidity level (from 50 to 90%) was carried out and its impact on gas sensing properties will be discussed.

        [1] T. R. Koehler, in Dynamical Properties of Solids, edited by G. K. Horton and A. A. Maradudin (North‐Holland, Amsterdam, 1975), Vol. 2, p. 3

        Speaker: Abderrahim Moumen (SENSOR Laboratory, University of Brescia, Via D. Valotti 9, 25133 Brescia, Italy)
      • 52
        Low-dimensional composite material based on modified graphene and metal oxide for high-performance chemical sensors

        Low-dimensional chemical sensors based on metal oxides have received great attention for the applications in security and medical diagnoses. Transition oxide nanomaterials exhibit promising sensing performance owing to their large surface area and good chemical stability. However, the sensing performance of these materials have yet to reach to their full potential in capabilities and usage. The fabrication of composite materials based on metal oxides is an effective way to enhance their sensing properties. TiO2 nanotubes (TNTs) have received extensive attention for gas sensing applications due to their large surface area, unique physical and chemical properties. Graphene with its modified forms, high specific surface area and excellent electronic properties can revolutionize performances of the functional devices. Herein, we report an efficient strategy to improve the sensing properties of TNTs. We fabricated composite structures by coupling of TNTs and modified-graphene. The morphological, structural and elemental analyses of samples were carried out. The sensing properties of obtained materials were tested towards H2, NH3, CO, ethanol and acetone (Fig. 1). We studied the effect of each material on the sensing performance of composite structures. The studies have shown the variation of mixture material concentration and the modification of graphene layers have a crucial effect on the response and the selectivity of the obtained composite materials. The obtained results demonstrate that we have developed an efficient method for the preparation of composite structures and the obtained materials can be applied for the fabrication of high-performance sensing systems.

        Speaker: Vardan Galstyan (Sensor Lab, Department of Information Engineering, University of Brescia)
      • 53
        Colloidal quantum dots for low-power-consumption semiconductor gas sensors

        Gas sensors are becoming increasingly important to the safety and quality of human life. In the past decades, semiconductor gas sensors employing high-temperature ceramics technology have been intensively investigated and higher senstivity as well as selectivity have been achieved. Silicon-based micro-electro-mechanical system (MEMS) hotplates have also been utilized to reduce both the volume size and power consumption of semiconductor gas sensors. Collodial quantum dots (CQDs) possess highly sensitive and programmable surface, combined with excellent solution processability, which make them ideal building blocks for next-generation gas sensors compatible with silicon-based or flexible substrates. Through the controllable systhesis with surface and interface enginnering strategy of CQDs, we have demonstrated senstive and selectve semiconductor gas sensors with lower power cosumption based on metal sulfides [1,2] and oxides [3,4], respectively. In addtion to traditional rigid substrates including ceramics and Si-based MEMS hotplates, soft substrates being flexible and stretchable were sucssfully used for the CQD gas sensors, which may open up a powerful new degree of freedom to semiconductor gas sensors being more intellegient and integratable.

        Speaker: Huan Liu
    • Invited Talk
      • 54
        Multiscale modelling of complex dynamical processes in solids with MBN Explorer and MBN Studio

        The multiscale modeling of complex molecular systems is a hot topic of the modern theoretical and computational research. To fully understand the dynamics of molecular systems and exploit it in different technological applications, such as hadron therapy, surface deposition and nanofabrication technologies, construction of novel light sources and others, one needs to consult many disciplines ranging from physics and chemistry to materials and life sciences, software engineering and high performance computing.
        The MBN Explorer software package [1] is powerful and universal instrument of computational research that allows to build up, with the help of implemented algorithms operating at different space-and-time scales, multiscale models for the description of various molecular systems and processes therein for numerous biomedical and nanotechnology applications [2]. MBN Studio [3] is a graphical user interface for MBN Explorer that has been developed to facilitate setting up and starting MBN Explorer calculations, monitoring their progress and examining the calculation results.
        There are several research areas in which multiscale simulations performed with the use of MBN Explorer and MBN Studio play an important role, constructing of novel light sources based on charged particles propagation in crystalline undulators [4]. The talk will present novel theoretical and computational approaches and methodologies implemented in MBN Explorer and MBN Studio as well as related case studies.

        Speaker: A. V. Korol (MBN Research Center, Altenhöferallee 3, 60438 Frankfurt am Main, Germany)
    • Morning Session 2: Chair: Vincenzo Guidi (University of Ferrara (Italy))
      • 55
        Channeling experiments at the Mainz Microtron MAMI

        The electron accelerator MAMI is multilevel racetrack microtron with a beam energy from 180 MeV up to 1.6 GeV and a continiuous beam current of more than 20 µA. The excellent beam quality due to the low emittance in transveral and longitudinal direction is well suited for channeling experiments and related radiation investigations.
        The possibility to produce undulator-like radiation in the hundreds of keV up to the MeV region by means of channeling in periodically bent crystals is well known (see [1] for a review). The usual schemes of making crystalline undulators involve some method of bending the planes or axes of the crystal, altering the usual channeling. One scheme, the large-amplitude, large-period, bends the planes such that the bending amplitude and period of the planes are significantly larger than the amplitude and period of the channeling motion. A second scheme consists of having a short-amplitude, short-period configuration. The bending of the planes only slightly perturbs the channeling motion trajectory, leading to increased radiation emission at higher photon energies than the usual channeling radiation.
        In recent years, experiments have been carried out at MAMI to investigate the radiation emission of channelled electrons in periodically bent silicon and diamond crystals. The results will be discussed for several epitaxially grown strained layer Si1-xGex crystals and boron doped diamond crystals at electron beam energies between 270 and 855 MeV.
        [1] W. Greiner, A.V. Korol, A.V. Solov’yov, Channeling and Radiation in Periodically Bent Crystals, (Springer, 2012).

        Work supported by the European Commission (the PEARL Project within the H2020-MSCA-RISE-2015 call, GA 690991).

        Speaker: Werner Lauth (Institut für Kernphysik, Johannes Gutenberg-Universität, D-55099 Mainz, Germany)
    • 10:30 AM
      Coffee Break
    • Invited Talk
      • 56
        Advanced Channeling Technologies: Strong External Electromagnetic Fields to Guide Charged & Neutral Beams

        Channeling is the phenomenon well-known in the physics world mostly related to the propagation of the beams of charged particles in aligned crystals. Since the beginning of 1970s channeling of high-energy leptons (electrons/positrons of several MeV up to hundred of GeV energies) and hadrons (protons/ions of tens GeV up to several TeV energies) has been applied at various famous world research centres within different national/international projects related to the phenomenon utilization to shape the beams as well as to produce high power x-ray and gamma radiation sources.
        However, recent studies have shown the feasibility of channeling phenomenology application for description of other various mechanisms of interaction of charged as well as neutral particles beams in solids, plasmas and electromagnetic fields covering the research fields from crystal/laser/plasma based undulators and collimators to capillary based x-ray and neutron optical elements.
        This review talk is devoted to actual channeling-based projects that have been realizing since so-called renessiance of channeling studies started in the end of last century. The future possible developments in channeling physics will be analyzed within the presentation.

        Speaker: Sultan B. Dabagov
    • Morning Session 2: Chair: Vincenzo Guidi (University of Ferrara (Italy))
      • 57
        Incoherent scattering reduction in crystals

        Despite the large strength of the coherent effects of particle deflection and radiation in crystals, all their applications are essentially limited by the incoherent scattering process. Though the difference of the latter from the scattering process in amorphous media was, in fact, envisaged by both the x-ray diffraction and coherent bremsstrahlung theories, the relational effect of multiple scattering reduction in crystals is scarcely known, has not been clearly observed, despite some attempts, and is usually missed in interpretation of the abundant experimental data. At the same time, this effect is presently important for the problems of particle deflection by long crystals, for both channeling and crystal undulator radiation, etc., and needs to be implemented in theory.
        Since multiple scattering reduction arises in crystals due to correlations of particle collisions with the strings or plane atoms, it can be observed at any high energy in the wide angular regions. At the same time, this effect can be clearly observed only under the rear conditions of any coherent scattering effect complete suppression. To reveal the latter, we applied the quantum Born approximation theory, being also equivalent to the classical one in straight trajectory approximation, and found a particular conditions of particle incidence at the angles of 2 degree and 3 mrad with respect to the ‹001› axis and (110) plane of Si crystal respectively, making possible to observe the multiple scattering reduction under the complete absence of coherent scattering, as Fig. 1 illustrates.
        [1] V.V. Tikhomirov, Phys. Rev. Acc. and Beams 22, 054501 (2019).

        Speaker: Victor Tikhomirov (Institute for Nuclear Problems)
      • 58
        Potential of parametric x-rays for application in particle identification detectors

        Cerenkov counters and transition radiation detectors are particle identification detectors (PID) used in many HEP experiments [1, 2]. Study and development of new accelerator facilities such as Future Circular Colliders (CERN), NICA (JINR) and others formulate new needs for particle identification in conditions of very high energies and luminosities. Parametric x-rays (PXR) [3] have big potential to be applied in particle identification detectors as radiation mechanism combining many properties of Cerenkov radiation and transition radiation in high kinematics range γ>1000. PXR mechanism well developed to date, both theoretically and experimentally. Many experiments were performed with electron beams. Key experiment with first observation of PXR from 70 GeV protons was reported in [4]. Later, PXR has been studied with 5 GeV protons and 2.2 GeV/u carbon nuclei in a silicon crystal on the external beams of the Nuclotron at JINR [5] and with 400 GeV/c protons in bent crystals at CERN SPS [6].
        So, we may state, that the community reached good understanding of the PXR properties by now and it is ready for the feasibility study of PXR application in particle identification. In contribution we will present and discuss characteristic features of PXR potentially applicable for PID including time dependences as timing requirements are of high importance for future colliders due to their increased collision rates. As first step for PXR application for high energy particle detection, implementation of PXR simulation tool to the GEANT4 toolkit can be proposed.
        [1] P. Krizan, Nucl. Instrum. Meth. A 581 (2007) 57.
        [2] A. Andronic, J.P.Wessels, Nucl. Instrum. Meth. A 666 (2012) 130.
        [3] V.G. Baryshevsky, I.D. Feranchuk, A.P. Ulyanenkov Parametric X-ray Radiation in Crystals: Theory, Experiments and Applications, Springer, 2005.
        [4] V.P. Afanasenko et al., JETP Lett. 54 (1991) 494.
        [5] Yu.N. Adishchev et al., Nucl. Instrum. Meth. B 252 (2006) 111.
        [6] W. Scandale et al. Physics Letters B 701 (2011) 180.

        Speaker: Alexander Lobko (Institute for Nuclear Problems)
      • 59
        Progress towards an experiment for electromagnetic dipole moments of unstable particles at the LHC

        A unique program of measurements of electric and magnetic dipole moments of unstable
        particles at the LHC, based on the phenomenon of spin precession of channeled particles in
        bent crystals, is presented [1, 2]. The ongoing R&D, feasibility studies, and the physics reach
        for the proposed experiment based on the LHCb detector are discussed, along with future
        perspectives for the tau lepton [3].
        [1] F. J. Botella et al., Eur.Phys.J. C77:181 (2017).
        [2] E. Bagli et al., Eur.Phys.J. C77:828 (2017).
        [3] J. Fu et al., Phys. Rev. Lett. 123, 011801 (2019).

        Speaker: Nicola Neri (Università degli Studi di Milano and INFN Milano)
      • 60
        Novel type of compact e.m. calorimeter based on oriented crystals for high-energy physics and astrophysics

        Twenty years ago at CERN it was demonstrated that the strong crystalline field of a single-element crystal, e.g. Si or W, may lead to a huge decrease in the shower length, if the beam direction is aligned with the crystal axes. Recently, we extended these studies to high-Z scintillator crystals typically exploited in electromagneticcalorimeters used in HEP and astrophysics. In particular, we measured a strong radiation length reduction for 120 GeV electrons interacting with a lead tungstate crystals (PWO) [1], demonstrating an increase of a factor 2 of the scintillation peak in case of axial alignment as compared to random orientation (see figure).

        The effect of shower length reduction can be exploited to develop an innovative type of electromagnetic calorimeter based on oriented scintillator crystals with the key feature of a reduced volume w.r.t. the state of the art. To demonstrate this possibility we developed a dedicated a Geant4 simulation package [2].
        These results open the way for a variety of applications in High-Energy Physics and Astrophysics. Such applications span from forward calorimeters/preshowers, to compact active beam dumps for the search for light dark matter, to pointing-strategy in satellite-borne gamma-ray telescope to decrease the required size to fully contain the e.m. shower generated by GeV to TeV particles.

        [1] L. Bandiera et al, Phys. Rev. Lett. 121 (2018) 021603
        [2] L. Bandiera et al, Nucl. Inst. Meth. Phys. Res. A, 936 (2019) 124

        • On behalf of the ELIOT experiment
        Speaker: Laura Bandiera (Istituto Nazionale di Fisica Nucleare (INFN) Sezione di Ferrara, Via Saragat 1 Ferrara, Italy)
    • 12:40 PM
    • Invited Talk
      • 61
        Using patchy particles to shed new light on the autocatalytic aggregation of soft matter

        Autocatalysis, i.e., the speeding up of a reaction through the very same molecule which is produced, is common in chemistry, biophysics, and material science. Despite the pervasiveness of autocatalytic phenomena in nature and technology, autocatalytic aggregation has so far remained out of reach of realistic numerical simulations. Rate-equation-based approaches are often used to model the time dependence of products, but the key physical mechanisms behind the reaction cannot be properly recognized and taken into account. On the contrary, patchy particles are designed learning from nature and can be thought of as an archetype of real monomers, so far they completely lack autocatalysis. Here, building on previous studies on the subject [1-4], we report on a patchy particle model inspired by a bicomponent reactive mixture and endowed with adjustable autocatalytic ability [5]. Such a coarse-grained model captures all general features of an autocatalytic aggregation process that takes place under controlled and realistic conditions, including crowded environments. Simulation reveals that a full understanding of the kinetics involves an unexpected effect that eludes the chemistry of the reaction, and which is crucially related to the presence of an activation barrier. The resulting analytical description can be exported to real systems, as confirmed by experimental data on epoxy–amine polymerizations, solving a long-standing issue in their mechanistic description.

        [1] S. Corezzi, C. De Michele, E. Zaccarelli, D. Fioretto and F. Sciortino, Soft Matter 4, 1173–1177 (2008)
        [2] S. Corezzi, C. De Michele, E. Zaccarelli, P. Tartaglia and F. Sciortino, J. Phys. Chem. B 113, 1233–1236 (2009)
        [3] S. Corezzi, D. Fioretto, C. De Michele, E. Zaccarelli and F. Sciortino, J. Phys. Chem. B 114, 3769–3775 (2010)
        [4] S. Corezzi, D. Fioretto and F. Sciortino, Soft Matter 8, 11207–11216 (2012)
        [5] S. Corezzi, F. Sciortino and C. De Michele, Nat. Commun. 9:2647 (2018)

        Speaker: Silvia Corezzi (University of Perugia)
    • Afternoon Session 1: Riccardo Cucini (CNR-IOM - Istituto Officina dei Materiali, Trieste (Italy))
      • 62
        Nucleation in Aqueous KCl Solutions Induced by Laser Pulses

        The nucleation processes are still today between the more intriguing problems of the condensed matter physics; they have been described by different models, but their understanding I still far to be complete [1]. In particular, we are missing the experimental investigations of the first nucleation events due to their unpredictable localization in the time and space coordinates.
        The nucleation in saturated solutions can be induced by a short laser pulse of high intensity [2]; a series of experimental studies have proved that this phenomenon occur in aqueous solutions of very different nature, where the solutes can vary from simple salts to complex biological molecules [3]. Even if the NonPhotochemical Laser Induced Nucleation (NPLIN) is known from more than 20 years, several fundamental aspects of it remain open problems [4]. Nevertheless, the NPLIN enables the possibility to perform spectroscopic measurements during the first steps of crystal nucleation and growth, opening the harvesting of new valuable information on this elusive phenomenon.
        We performed an experimental investigation of the nucleation phenomena induced by a 25 picosecond infrared laser pulse in a supersaturated aqueous KCl solution. In particular, we developed an experimental set-up able to perform a very fast imaging (up to 5*105 frame/sec) of the solution modifications induced by the laser pulse. The fast imaging shows a series of physical processes taking place in the solution between the laser pulse arrival and the show up of the crystal nucleus.
        [1] Kelton, K. F.; Frenkel, D. Preface: Journal of Chemical Physics 2016, 145 (21).
        [2] Garetz, B. A.; Aber, J. E.; Goddard, N. L.; Young, R. G.; Myerson, A. S. Physical Review Letters 1996, 77 (16), 3475.
        [3] Li, W.; Ikni, A.; Scouflaire, P.; Shi, X.; El Hassan, N.; Gémeiner, P.; Gillet, J.-M.; Spasojević-de Biré, A. Cryst Growth Des 2016, 16 (5), 2514.
        [4] Kacker, R.; Dhingra, S.; Irimia, D.; Ghatkesar, M. K.; Stankiewicz, A.; Kramer, H. J. M.; Eral, H. B. Cryst Growth Des 2018, 18 (1), 312.

        Speaker: Renato Torre (European Laboratory for Non-Linear Spectroscopy (LENS), Università di Firenze, Italy; Dip. di Fisica ed Astronomia; Università di Firenze, Italy)
      • 63
        Dynamical properties of ice and water: a broadband dielectric spectroscopy study

        Though the mechanical properties of ice and water differ, they still have much in common from the dielectric spectroscopy viewpoint. We analyze the spectra of dynamical conductivity of solid and liquid water as a signature of their molecular dynamics. The dynamics of ice and water are considered on the same footing. We introduce a model [1] that provides a clear interpretation of the experimental conductivity and dielectric constant over fourteen orders of frequency magnitude, thus extending the scope of the existing models. The model links together infrared vibrations with static conductivity and dielectric constant, gives the interplay between the electrical and thermodynamic properties of ice and water, and provides a new dynamical vision on the old problem of the water structure.

        [1] V. Artemov, Phys. Chem. Chem. Phys. 21, 8067 (2019).

        Speaker: Vasily Artemov (Skolkovo Institute of Science and Technology)
    • Invited Talk
      • 64
        Hertz-to-terahertz dielectric response of nanoconfined water molecules

        Recently, considerable attention has been given to the properties of systems that contain interacting point electric dipoles. Such systems are expected to manifest rich variety of exotic phases resulting from competition between the dipole-dipole coupling and disordering effects, both dependent of various factors, like spatial symmetry and dimensionality of the dipoles locations, presense of defects and impurities, frustration, etc. An additional issue concerns the study of the dynamics of dipoles as interacting quantum rotors that experience a multi-well localizing potential in presence of hindering effects and quantum rotational tunneling. It is important, that the electro-static coupling among the dipoles makes such systems qualitatively different from their magnetic counterparts. Since interacting spins have been thoroughly studied during last decades, significant progress has been achieved in understanding the underlying magnetic physics. In electric dipolar systems, the interplay of quantum tunneling, fluctuations and frustration provides with the possibility to realize new exotic phases, like (anti)ferroelectricity, quantum electric dipolar liquids and glasses, lead to quantum critical phenomena and quantum phase transitions. Understanding the nature of the corresponding phases, their formation and relations with magnetic counterparts is of great fundamental and technological interest, but is presently at its infancy.
        Prospective playground for corresponding studies is provided by dielectrics whose crystal lattice contains voids filled with electric-polar molecules that only weakly interact with surrounding ions and are thus nearly free, but “feel” each other via long-range electric dipole-dipole interaction. Corresponding broad-band spectroscopic studies of the gemstone beryl with 0.5 nm sized pores hosting polar H2O molecules (each carrying a dipole moment of ≈1.85 Debye) allowed to discover incipient ferroelectricity within the H2O dipoles, along with a rich set of single-particle excitations at terahertz-infrared frequencies [1-5]. It was suggested that the (anti)ferroelectric phase transition into the macroscopically ordered state was suppressed by quantum tunnelling of H2O molecules between 1 meV deep wells of the localizing six-fold potential. Here, we present detailed spectroscopic studies of single-particle and collective vibrational states of a network of H2O molecules hosted by orthorhombic crystal lattice of cordierite. Unlike hexagonal beryl, water molecules in cordierite experience 2-well localizing potential while rotating 360° around the c-axis, with the wells separated by an order of magnitude higher energy barriers of ≈10 meV.
        Using terahertz (THz), radio-frequency (RF) and microwave (μW) spectroscopies, we measure polarization-dependent (E-field component of the probing radiation parallel to a, b and c axes) spectra of the complex dielectric permittivity ε(ν)=ε'(ν)+iε"(ν) and AC conductivity σ(ν)=σ1(ν)+iσ2(ν) of hydrous cordierite in the range ν=1 Hz – 3 THz and at temperatures 0.3 K – 300 K. Measurements on water-free (annealed in vacuum) crystals allowed us to extract the spectra determined exclusively by water molecules. In the THz range, 0.3 THz – 3 THz, rich sets of highly anisotropic soft excitations are discovered. Applying density-functional and molecular dynamics analyses allowed us to associate the origin of the excitations with complex librational-rotational vibrations of the nanoconfined polar water molecules. In the RF- μW ranges, 1 Hz – 1 GHz, for the E||a polarization we discover a strongly temperature-dependent overdamped excitation and assign its origin to relaxational dynamics of separate molecular dipoles within the confining cage. Below 3 K, we detect weak signatures of a phase transition into a glassy state formed by frozen water dipoles. We will perform comparative analysis of the results obtained on water dipoles arranged in hexagonal (beryl matrix) and in orthorhombic (cordierite matrix) arrays.
        Authors acknowledge support from RFBR grants 18-32-00286 and 18-32-20186, DFG via DR228/61-1 and Center of Integrated Quantum Science and Technology IQST Stuttgart/Ulm.
        [1]. B.P.Gorshunov et al., J. Physical Chemistry Letters, 4, 2015 (2013).
        [2]. B.P.Gorshunov et al., Nature Communications, 7, 12842 (2016).
        [3]. M.A.Belyanchikov et al., Physical Chemistry Chemical Physics, 19, 30740 (2017).
        [4]. E.S.Zhukova et al. EPJ Web of Conferences, 195, 06018 (2018).
        [5]. M.Dressel et al., J. Infrared, Millimeter and Terahertz Waves, 39, 799 (2018).

        Speaker: B. Gorshunov (Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, 141700 Russia)
    • Afternoon Session 1: Riccardo Cucini (CNR-IOM - Istituto Officina dei Materiali, Trieste (Italy))
      • 65
        Tuning the fast dynamics of PNIPAM-based systems with bio-cosolvents

        Responsive polymers as poly-N-isopropylacrylamide (PNIPAM) are known as “smart”
        materials due to their ability to respond to variations of parameters like temperature, pH,
        pressure, and many others. PNIPAM phase behaviour results from a highly temperaturesensitive competition between hydrophobicity of methyl and methylene groups and the
        ability of amide groups to make strong hydrogen bonds. When the temperature increases
        above a critical value (lower critical solution temperature, LCST), molecular agitation
        disrupts hydrogen bonds and leads to the breakdown of the local structure of water around
        PNIPAM chains. PNIPAM can be arranged in 3-D networks in order to form microgel
        particles which in correspondence of a critical temperature pass from a swollen, hydrated
        phase to a collapsed, dehydrated one, giving rise to the so-called Volume Phase Transition
        (VPT). Different environments can impact on this delicate balance between hydrophilic and
        hydrophobic interactions and strongly affect the LCST [1]. It is interesting to look at the
        transition of PNIPAM as an analogous to the cold denaturation of proteins: at high
        temperature PNIPAM is in a globular, folded state, but it unfolds to a coil as it is cooled
        below a critical temperature. It is known that changes of the environment by the addition of
        cosolvents has an impact on the protein behaviour, as they can act as cryopreservant (e.g.,
        DMSO), denaturant (e.g., ethanol), stabilizer (e.g. glycerol) [2]. Despite the great interest in
        the understanding of the mechanisms underlying these effects, they are not yet completely
        understood. In this context, we use a multi-technichal approach to study how different
        solvent mixtures affect the PNIPAM hydration states and correlate with changes in the
        structure of PNIPAM-based microgel particles across the VPT. We use UV-Raman and
        neutron scattering measurements to get microscopic dynamical information to be correlated
        to macroscopic structural information obtained by PCS.
        [1] D. Mukherji, C. M. Marques, K. Kremer, Nat. Commun. 5, 4882 (2014)
        [2] A. Paciaroni, E. Cornicchi, A. De Francesco, M. C. Marconi, G. Onori, Eur. Biophys. J.
        35, 591 (2006)
        [3] M. Zanatta, L. Tavagnacco, E. Buratti, M. Bertoldo, F. Natali, E. Chiessi, A. Orecchini, E.
        Zaccarelli, Sci Adv 4, eeat5895 (2018)

        Speaker: Benedetta Petra Rosi (University of Perugia)
      • 66
        Molecular dynamics of a liquid crystal with highly ordered smectic E phase under different forms of confinement

        Liquid crystals (LCs) confined in various host system have attracted great interest in recent years. New material properties originating from finite size of pores and interaction between molecules and pore surface have been reported, including optical properties, dynamic peculiarities and different phase diagram than in bulk. It was concluded that a change in the transition temperature origins from two competing effects: orientational order locally imposed by pore surface that increases the transition temperature and disordering effect resulting from the elastic forces and rearrangement of defect lines which cause the reduction of the transition temperature. One of our previous papers [1,2] discusses the dynamics and morphology of 4-heptyl-4’- isothiocyanatobiphenyl (7BT) confined in silica pores with average diameters of 4, 6, 7.5, 9.5 and 10.5 nm. While 7BT in bulk demonstrates a smectic E (SmE) phase characterized by an orthorhombic arrangement of molecules within the smectic layers, the order of 7BT molecules is imposed by a strong surface potential in nanopores. Consequently, molecular dynamics are significantly modified in nanopores compared to bulk. Two relaxation processes were detected by dielectric spectroscopy: one related to the “flip-flop” motions of molecules around their short axis, while the second was ascribed to the librational motions of molecules partially immobilized on pore walls. As the pore size decreases, the surface effect becomes more pronounced, with only librational motions observed in 4nm pores. An analysis of the temperature dependencies of specific IR absorption bands, in terms of their spectral position and integrated intensity, highlighted the varied influence of confinement on rigid and flexible molecular moieties: i.e. the gradual ordering of aromatic cores and amorphous-like behaviour of alkyl chains.
        The purpose of this work is to exam the dynamic properties of 4-hexyl-4′-isothiocyanatobiphenyl (6BT) with a SmE phase experiencing different forms of confinement. Hard confinement was achieved by the infiltration of LCs into nanoporous aluminum oxide (AAO) templates with non-intersecting, cylindrical, channels. Other interesting, but as yet unexplored is soft confinement derived from the interactions between the polymer and guest liquid crystalline molecules. This was investigated on an example of electrospun polymer/liquid crystal composite fibers (see Fig. 1). We prepared composite fibers for three different mass ratios of polycaprolactone (PCL) and 6BT. By a combination of broadband dielectric spectroscopy and Fourier-Transform Infrared (FTIR), the microscopic picture of the influence of soft and hard confinement on molecular dynamics is obtained. In this talk, I will discuss similarities and differences in the impact of hard and soft confinement on dynamic properties and crystallization kinetics of 6BT liquid crystal.

        Fig.1 Sketch showing formation of composite PCL/6BT composite electrospun fibres.

        1 M. Jasiurkowska, W. Kossack, R. Ene, C. Iacob, W. K. Kipnusu, P. Papadopoulos, J. R. Sangoro, M. Massalska-Arodź, F.Kremer, Soft Matter 8 (19), 5194 (2012).
        [2] W.K. Kipnusu, C. Iacob, M. Jasiurkowska-Delaporte, W. Kossack, J. R. Sangoro, F. Kremer; “Rotational diffusion of guest molecules confined in uni-directional nanopores” in: Dynamics in Geometrical Confinement, F. Kremer (Ed.), Springer-Verlag (2014)
        M. J-D acknowledges the National Science Centre (Grant SONATA11: UMO-2016/21/D/ST3/01299) for financial support.

        Speaker: Malgorzata Jasiurkowska-Delaporte (Institute of Nuclear Physics, Polish Academy of Sciences)
    • 3:50 PM
      Coffee Break
    • Closing and Award Ceremony