Strongly interacting electrons can move in a neatly coordinated way, reminiscent of the movement of viscous fluids. In viscous electron flows interactions lead to unusual collective behavior such as vortices and negative resistance. This talk will focus on superballistic conduction of viscous electron flows in which interactions facilitate transport and allow conductance to exceed the fundamental Sharvin-Landauer ballistic limit. We will describe a theory of the ballistic-to-viscous crossover in a constriction exhibiting the ballistic transport at zero temperature but governed by electron hydrodynamics at elevated temperatures. We will also discuss recent measurements of electron transport through graphene constrictions, finding that conductance below 150 K increases with increasing temperature. The measurements help to identify the contribution to conductance arising due to electron viscosity and determine its temperature dependence. Besides fundamental interest, this work shows that viscous effects can facilitate high-mobility transport at elevated temperatures, a potentially useful behavior for designing graphene-based devices.
Leonid S. Levitov ist Professor für Physik am Massachusetts Institute of Technology (MIT) und derzeit Visiting Fellow am CAS.