Frequent collisions between constituents in a classical or quantum liquid (like 3He) manifest through a transport coefficient called the shear viscosity . The flow of these liquids, and also that of exotic quantum many-particle systems like ultracold 6Li atoms near a Feshbach resonance  and quark-gluon plasmas at relativistic heavy-ion colliders , is often described by three equations expressing the conservation of mass, momentum (the Navier-Stokes equation), and energy.
Realizing hydrodynamic transport in a solid has proven challenging, because of ever present processes that lead to momentum dissipation in the electron subsystem . Even when suitable conditions are met, key questions have remained largely unexplored : how do you diagnose the emergence of hydrodynamic electron flow in a conventional field-effect transistor ? How do you measure the viscosity of an electron liquid in such a setup ? What is the impact of viscosity on electron transport ?
In this talk I will try and answer these questions. I will report on results of combined theoretical and experimental work [5,6,7] showing unambiguous evidence for the long-sought hydrodynamic solid-state 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 [5,6,7]. Measurements of these non-local electrical signalsallow to extract the value of the kinematic viscosity of the two-dimensional electron liquid in graphene, which is found to be an order of magnitude larger than that of honey and to compare well with many-body theoretical predictions .
Finally, if time allows, I will discuss recent developments in my group, including a study of viscous electron transport across point contacts and ideas on how to probe hydrodynamic behavior via the use of engineered short-wavelength plasmon-phonon polaritons in hybrid stacks containing graphene, Boron Nitride, and metal gates.
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Marco Polini graduated in Theoretical 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). He has been a postdoctoral fellow in the group of Prof. Allan MacDonald at the University of Texas at Austin (USA) and a permanent staff member of the Nanoscience Institute of the Italian National Research Council (2008-2015) in Pisa (Italy). From September 1, 2015 he holds a Senior Scientist position 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 in 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 at 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 A&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 NUS Centre for Advanced 2D Materials and Graphene Research Centre in Singapore, at the Massachusetts Institute of Technology (USA), at the Institute of Photonic Sciences – ICFO (Spain), and at the University of Manchester (UK). In 2010 he was awarded with the prestigious Italian grant “FIRB - Futuro in Ricerca”.