On the universal AC optical background in graphene

TL;DR

This paper provides analytical formulas for graphene's ac conductivity, exploring how interactions, temperature, magnetic fields, and gaps influence its universal value, with implications for metrology and quasiparticle dynamics.

Contribution

It introduces new analytical expressions for graphene's ac conductivity considering various effects, advancing understanding beyond idealized models.

Findings

AC conductivity oscillates around the universal value in magnetic fields

Electron-phonon interactions deplete the ac conductivity

Drude peak shifts to cyclotron frequency in magnetic fields

Abstract

The latest experiments have confirmed the theoretically expected universal value $\pi e^2/2h$ of the ac conductivity of graphene and have revealed departures of the quasiparticle dynamics from predictions for the Dirac fermions in idealized graphene. We present analytical expressions for the ac conductivity in graphene which allow one to study how it is affected by interactions, temperature, external magnetic field and the opening of a gap in the quasiparticle spectrum. We show that the ac conductivity of graphene does not necessarily give a metrologically accurate value of the von Klitzing constant $h/e^2$, because it is depleted by the electron-phonon interaction. In a weak magnetic field the ac conductivity oscillates around the universal value and the Drude peak evolves into a peak at the cyclotron frequency.