Microscopic theory for electron hydrodynamics in monolayer and bilayer graphene

TL;DR

This paper develops a microscopic theory for electron hydrodynamics in monolayer and bilayer graphene, revealing two distinct regimes and explaining experimental observations of law violations through impurity effects.

Contribution

It introduces a detailed microscopic model for electron interactions in graphene, predicting different hydrodynamic regimes and explaining experimental anomalies.

Findings

Bilayer graphene exhibits a stronger hydrodynamic window than monolayer.

The hydrodynamic regimes have distinct 'v-shape' and 'lung-shape' characteristics.

Experimental data collapse onto a universal disorder-limited theory, explaining Wiedemann-Franz law violations.

Abstract

Electrons behave like a classical fluid with a momentum distribution function that varies slowly in space and time when the quantum mechanical carrier-carrier scattering dominates over all other scattering processes. Recent experiments in monolayer and bilayer graphene have reported signatures of such hydrodynamic electron behavior in ultra-clean devices. In this theoretical work, starting from a microscopic treatment of electron-electron, electron-phonon and electron-impurity interactions within the Random Phase Approximation, we demonstrate that monolayer and bilayer graphene both host two different hydrodynamic regimes. We predict that the hydrodynamic window in bilayer graphene is stronger than in monolayer graphene, and has a characteristic `v-shape' as opposed to a `lung-shape'. Finally, we collapse experimental data onto a universal disorder-limited theory, thereby proving that the observed violation of Wiedemann-Franz law in monolayers occurs in a regime dominated by impurity-induced electron-hole puddles.