Valley hydrodynamics in gapped graphene

TL;DR

This paper develops a hydrodynamic theory for electrons in gapped graphene, incorporating valley degrees of freedom and dissipation, revealing new mechanisms for valley polarization and valley currents driven by microrotation effects.

Contribution

It introduces a micropolar fluid model for electron hydrodynamics in graphene, including valley angular momentum dissipation, and proposes a new method to generate valley polarization via microrotation.

Findings

Rotational viscosity induces longitudinal valley currents.

Valley polarization can be generated through microrotation.

The theory predicts second-order valley currents in electric fields.

Abstract

Recent experiments have revealed that novel nonequilibrium states consistent with the hydrodynamic description of electrons are realized in ultrapure graphene, which hosts the valley degrees of freedom. Here, we formulate a theory of electron hydrodynamics including dissipation processes of the valley angular momentum by employing the concept of micropolar fluids. As a result, our theory proposes a novel strategy to generate a valley polarization by the microrotation. We uncover that the rotational viscosity induces longitudinal valley currents which are second order in electric fields.