Speaker: Dr. Marco Polini
Affiliation: Italian Institute of Technology, Italy
Abstract Details: Graphene sheets encapsulated between crystals of hexagonal boron nitride host a unique two-dimensional (2D) electron system, whereby electrons suffer minimal scattering against acoustic phonons and practically no scattering against long-range disorder (unless gated very close to the charge neutrality point) [1-4]. Above liquid nitrogen temperatures, these electron liquids are expected to display local equilibrium enabled by strong electron-electron interactions and viscosity-dominated hydrodynamic transport [5-8].
In this talk I will report on results of combined theoretical and experimental work  showing unambiguous evidence for this long-sought transport regime. In particular, I will discuss how high-quality doped graphene sheets above liquid nitrogen temperatures exhibit negative non-local resistance near current injection points and whirlpools in the spatial current pattern [6,9,10]. Measurements of these non-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 compare well with many-body theoretical predictions . Finally, I will also discuss the subtle connection between negative non-local resistances and current whirlpools .
 A.S. Mayorov et al., Nano Lett. 11, 2396 (2011).
 L. Wang et al., Science 342, 614 (2013).
 T. Taychatanapat et al., Nature Phys. 9, 225 (2013).
 A. Woessner et al., Nature Mater. 14, 421 (2015).
 M. Polini and G. Vignale, The quasiparticle lifetime in a doped graphene sheet.Â 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).
 I. Torre, A. Tomadin, A.K. Geim, and M. Polini, Phys. Rev. B 92, 165433 (2015).
 A. Principi, G. Vignale, M. Carrega, and M. Polini, Phys. Rev. B 93, 125410 (2016).
 L. Levitov and G. Falkovich, Nature Phys. 12, 672 (2016).
 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).
 F.M.D. Pellegrino, I. Torre, A.K. Geim, and M. Polini, Phys. Rev. B 94, 155414 (2016).
About the Speaker: Marco Polini graduated in Physics in 1999 from the University of Pisa (Italy) and received his Ph.D. in Physics in January 2003 from the Scuola Normale Superiore (Pisa, Italy).Â
He is a Senior Scientist at the Istituto Italiano di Tecnologia (Italian Institute of Technology) in Genoa (Italy), where he leads the Theory and technology of 2D materials group.
He also holds a contract professorship at the Scuola Normale Superiore (Pisa, Italy). He has co-authored more than 140 publications in peer-reviewed international journals including Science, Nature Materials, Nature Nanotechnology, Nature Photonics, Nature Communications, and Physical Review Letters and he is a coauthor of the book Many-body physics in condensed matter systems (Edizioni della Normale, Pisa, 2006). He has carried out research at the University of Texas atÂ Austin (USA), at the Zhejiang Normal University (China), at the Chinese Academy of Sciences in Beijing (China), at Purdue University (USA), at the University of Missouri-Columbia (USA), at Texas ;M University (USA), at the Kavli Institute for Theoretical Physics in Santa Barbara (USA), at the University of New South Wales (Australia), at the Cambridge Graphene Center (UK), at the Graphene Research Center in Singapore, at the Massachusetts Institute of Technology (USA), and at the University of Manchester (UK). In 2010 he was awarded with the prestigious italian grant FIRB - Futuro in Ricerca