Viscosity Enhancement by Electron-Hole Collisions in Dirac Electron Fluid

TL;DR

This paper explores how electron-hole collisions can significantly enhance the viscosity of Dirac electron fluids in graphene, revealing new ways to amplify hydrodynamic effects in solid-state systems.

Contribution

It introduces a microscopic understanding of viscosity enhancement in Dirac electron fluids via electron-hole collisions, magnetic fields, and dynamic deformations, advancing hydrodynamic electronics research.

Findings

Electron-hole collisions increase shear viscosity in graphene.

Magnetic fields induce shared Landau levels affecting viscosity.

Dynamic deformation excites electron-hole pairs influencing hydrodynamics.

Abstract

Rejuvenation of hydrodynamic transport in solids provides a new window to study collective motion of electrons, where electrons behave like a viscous fluid akin to classical liquids. Experimental observations of such exotic states have not been realized until recent years, and an on-going quest is to amplify the hydrodynamic effect in electron fluids. Here we investigate the hydrodynamic properties of Dirac electron fluid in graphene from a microscopic viewpoint, and elucidate a novel way to enhance electron hydrodynamics. In particular, we present strong evidence that the shear viscosity of Dirac electrons can be enhanced by frequent electron-hole collisions, through three distinct aspects: promoting electrons and holes around the Dirac point by disorder, creating electron-hole shared zeroth Landau level by external magnetic field, and inducing electron-hole excitations by dynamic deformation. We also study Hall viscosity, which is closely related to the geometric topology and exhibits quantum behavior analogous to Hall conductivity. Therefore, our work demonstrates the exotic landscape of hydrodynamic electronics in graphene, and presents experimentally relevant responses to quantify the effects of electronic viscosity.