Hydrodynamic transport, laminar flow, and the AdS/CFT viscosity bound in a graphene field effect transistor
by
Marco Polini
→
Europe/Rome
248 (Building C, First Floor)
248
Building C, First Floor
Description
Graphene sheets encapsulated between crystals of boron nitride host a unique electron system that due to weak electron-phonon scattering allows micrometer-scale ballistic transport even at room temperature [1,2,3,4]. Above liquid nitrogen temperatures, these electron liquids are expected to display local equilibrium, enabled by strong electron-electron interactions [5]. Under these conditions, electrons in doped samples are expected to behave as a viscous liquid and may exhibit hydrodynamic phenomena akin to those observed in classical and quantum liquids. In this talk I will report on results of combined theoretical and experimental work [6,7] showing unambiguous evidence for this long-sought transport regime. In particular, I will discuss how high-quality graphene sheets in the Fermi liquid regime (k_B T ≲ E_F) exhibit an anomalous (negative) voltage drop near current injection points, which is attributed to the formation of whirlpools in the electron flow. Measurements of these quasi-local electrical signals enable to extract the value of the kinematic viscosity of the two-dimensional massless Dirac fermion liquid in graphene, which is found to be an order of magnitude larger than that of honey, in quantitative agreement with many-body theory [8]. Finally, I will discuss how our results near the charge neutrality point (k_B T≫ E_F) are compatible with the AdS/CFT viscosity bound [9,10].
Our work represents the first step towards the observation of nearly perfect fluidity and turbulence in solid-state devices.
References
[1] A.S. Mayorov et al., Nano Lett. 11, 2396 (2011).
[2] L. Wang et al., Science 342, 614 (2013).
[3] T. Taychatanapat et al., Nature Phys. 9, 225 (2013).
[4] A. Woessner et al., Nature Mater. 14, 421 (2015).
[5] M. Polini and G. Vignale, The quasiparticle lifetime in a doped graphene sheet. In No-nonsense physicist: an overview of Gabriele Giuliani's work and life (eds. M. Polini, G. Vignale, V. Pellegrini, and J.K. Jain) (Edizioni della Normale, Pisa, 2016).
[6] D. Bandurin, I. Torre, R.K. Kumar, M. Ben Shalom, A. Tomadin, A. Principi, G.H. Auton, E. Khestanova, K.S. NovoseIov, I.V. Grigorieva, L.A. Ponomarenko, A.K. Geim, and M. Polini, Science (February 11, 2016).
[7] I. Torre, A. Tomadin, A.K. Geim, and M. Polini, Phys. Rev. B 92, 165433 (2015).
[8] A. Principi, G. Vignale, M. Carrega, and M. Polini, Phys. Rev. B (2016) and arXiv:1506.06030.
[9] P.K. Kovtun, D.T. Son, and A.O. Starinets, Phys. Rev. Lett. 94, 111601 (2005).
[10] M. Müller, J. Schmalian, and L. Fritz, Phys. Rev. Lett. 103, 025301 (2009).