Negative dynamic Drude conductivity in pumped graphene

TL;DR

This paper predicts a new light amplification mechanism in pumped graphene due to negative interband Drude conductivity caused by indirect interband transitions involving disorder scattering.

Contribution

It introduces the concept of interband Drude conductivity and demonstrates its potential to enable optical gain in graphene at terahertz and near-infrared frequencies.

Findings

Negative net Drude conductivity can occur below double quasi-Fermi energy.

Radiation amplification exceeding 2.3% is possible in graphene.

The effect is prominent with Gaussian correlated disorder.

Abstract

We theoretically reveal a new mechanism of light amplification in graphene under the conditions of interband population inversion. It is enabled by the indirect interband transitions, with the photon emission preceded or followed by the scattering on disorder. The emerging contribution to the optical conductivity, which we call the interband Drude conductivity, appears to be negative for the photon energies below the double quasi-Fermi energy of pumped electrons and holes. We find that for the Gaussian correlated distribution of scattering centers, the real part of the net Drude conductivity (interband plus intraband) can be negative in the terahertz and near-infrared frequency ranges, while the radiation amplification by a single graphene sheet can exceed 2.3%.