Electron-phonon interactions in 2D materials studied by resonance and polarized Raman spectroscopy.

by Marcos A. Pimenta (Departamento de Fisica, Universidade Federal de Minas Gerais Belo Horizonte, Brasil)

Wednesday 6 Apr 2022, 16:00 → 18:00 Europe/Rome

Aula Conversi (Dip. di Fisica - Edificio G. Marconi)

In this seminar I will discuss the use of Raman spectroscopy to study phonons and electron-phonon interactions in 2D materials. I will start reviewing the Raman spectra of graphene, showing that measurements performed by changing the energy of the incident photon provide information about the electronic structure of the material. I will then focus on the resonance Raman effect in twisted bilayer graphene (TBG), presenting experimental results performed in TBG samples with different twisting angles that allow the distinction of intralayer and interlayer electron-phonon (el-ph) interactions [1], and theoretical calculations of the double-resonance (DR) Raman intensity in graphene by imposing the momentum conservation rules for these two el-ph processes [2]. I will then present results in 2D crystals of the transition metal dichalcogenide (TMD) family, starting with the semiconducting MoS₂ crystals where we could observe symmetry dependent el-ph interactions [3] and investigate the scattering of electrons by acoustic phonons between different valleys in the electronic structure [4].  Finally, I will present angle-resolved polarized Raman measurements in triclinic ReSe₂ and show that the Raman tensor elements for the different phonons are given by complex numbers due to the resonance effect. I will show that the wavevector dependence of the electron–phonon interaction is essential for explaining the distinct results observed for each phonon mode [5].

1. G. S. N. Eliel et al, Nature Comm 9, 1221 (2018)
2. M. V. O. Moutinho et al, Scientific Reports, 11, 1, 17206 (2021)
3. B. R, Carvalho et al, Phys. Rev. Letters 114, 136403 (2015)
4. B. R. Carvalho et al, Nature Comm. 8, 14670 (2017)
5. G. C. Resende et al, 2D Materials 8, 025002 (2020)