Drude weight, plasmon dispersion, and pseudospin response in doped graphene sheets

TL;DR

This paper reveals that in doped graphene, plasmon frequency and Drude weight are significantly renormalized by many-body effects, unlike in ordinary electron liquids, due to non-local exchange interactions, challenging the predictions of RPA.

Contribution

It demonstrates the strong renormalization of plasmon and Drude weight in doped graphene beyond RPA, highlighting the role of non-local exchange interactions.

Findings

Plasmon frequency is reduced relative to RPA predictions.

Drude weight is decreased due to exchange interactions.

Renormalizations are observable via spectroscopy techniques.

Abstract

Plasmons in ordinary electron liquids are collective excitations whose long-wavelength limit is rigid center-of-mass motion with a dispersion relation that is, as a consequence of Galileian invariance, unrenormalized by many-body effects. The long-wavelength plasmon frequency is related by the f-sum rule to the integral of the conductivity over the electron-liquid's Drude peak, implying that transport properties also tend not to have important electron-electron interaction renormalizations. In this article we demonstrate that the plasmon frequency and Drude weight of the electron liquid in a doped graphene sheet, which is described by a massless Dirac Hamiltonian and not invariant under ordinary Galileian boosts, are strongly renormalized even in the long-wavelength limit. This effect is not captured by the Random Phase Approximation (RPA), commonly used to describe electron fluids. It is due primarily to non-local inter-band exchange interactions, which, as we show, reduce both the plasmon frequency and the Drude weight relative to the RPA value. Our predictions can be checked using inelastic light scattering or infrared spectroscopy.