Electron hydrodynamics dilemma: whirlpools or no whirlpools

TL;DR

This paper investigates how the geometry of viscous electron systems influences the formation of whirlpools, revealing that confinement and contact placement are crucial factors determining their emergence.

Contribution

It demonstrates that geometry and contact positioning critically affect whirlpool formation in viscous electron flows, highlighting conditions for their appearance at various viscosities.

Findings

Geometry and contact placement determine whirlpool formation.

Certain geometries can exhibit whirlpools at very low viscosities.

Threshold conditions for whirlpools depend on device design.

Abstract

In highly viscous electron systems such as, for example, high quality graphene above liquid nitrogen temperature, a linear response to applied electric current becomes essentially nonlocal, which can give rise to a number of new and counterintuitive phenomena including negative nonlocal resistance and current whirlpools. It has also been shown that, although both effects originate from high electron viscosity, a negative voltage drop does not principally require current backflow. In this work, we study the role of geometry on viscous flow and show that confinement effects and relative positions of injector and collector contacts play a pivotal role in the occurrence of whirlpools. Certain geometries may exhibit backflow at arbitrarily small values of the electron viscosity, whereas others require a specific threshold value for whirlpools to emerge.