Hydrodynamic model for electron-hole plasma in graphene

TL;DR

This paper develops a hydrodynamic model for electron-hole plasma in graphene, capturing transport, collective excitations, and mutual drag effects, applicable to both bipolar and monopolar regimes, with implications for conductivity and plasma wave behavior.

Contribution

It introduces a novel hydrodynamic framework that accounts for electron-hole interactions and spectra in graphene, extending understanding of plasma dynamics and transport properties.

Findings

Model accurately describes graphene conductivity including electron-hole drag.

Identifies conditions for electron-hole sound waves and plasma excitations.

Shows excitations depend on gate voltage and carrier densities.

Abstract

We propose a hydrodynamic model describing steady-state and dynamic electron and hole transport properties of graphene structures which accounts for the features of the electron and hole spectra. It is intended for electron-hole plasma in graphene characterized by high rate of intercarrier scattering compared to external scattering (on phonons and impurities), i.e., for intrinsic or optically pumped (bipolar plasma), and gated graphene (virtually monopolar plasma). We demonstrate that the effect of strong interaction of electrons and holes on their transport can be treated as a viscous friction between the electron and hole components. We apply the developed model for the calculations of the graphene dc conductivity, in particular, the effect of mutual drag of electrons and holes is described. The spectra and damping of collective excitations in graphene in the bipolar and monopolar limits are found. It is shown that at high gate voltages and, hence, at high electron and low hole densities (or vice-versa), the excitations are associated with the self-consistent electric field and the hydrodynamic pressure (plasma waves). In intrinsic and optically pumped graphene, the waves constitute quasineutral perturbations of the electron and hole densities (electron-hole sound waves) with the velocity being dependent only on the fundamental graphene constants.