Joint ICTP/SISSA SP Seminar 22.04.2016 @ SISSA: Marco Polini

[Condensed Matter Section]

JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR

Friday 22 April - 14:00 hrs

SISSA, room 128

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Speaker: Marco Polini (Istituto Italiano di Tecnologia)

Title: Hydrodynamic transport, laminar flow, and the AdS/CFT viscosity
bound in a graphene field effect transistor

Abstract: 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 (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 ( are compatible with the AdS/CFT viscosity bound [9,10].
Our work represents the first step towards the observation of nearly
perfect fluidity and quantum 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 351, 1055 (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
93, 125410 (2016).
[9]	P.K. Kovtun, D.T. Son, and A.O. Starinets, Phys. Rev. Lett. 94,
111601 (2005).
[10]	M. Mueller, J. Schmalian, and L. Fritz, Phys. Rev. Lett. 103,
025301 (2009).