Nonlinear optical response in gapped graphene

TL;DR

This paper develops a theoretical framework for the nonlinear optical response in gapped graphene, revealing how the optical nonlinearity can be enhanced by tuning the energy gap, with specific results for third harmonic generation.

Contribution

It introduces a covariant formulation for the nonlinear optical response in gapped graphene and derives a closed-form expression for third harmonic generation.

Findings

Logarithmic singularities in nonlinear spectra

Universal response dependence on dimensionless parameters

Enhanced nonlinearity with smaller energy gaps

Abstract

We present a formulation for the nonlinear optical response in gapped graphene, where the low-energy single-particle spectrum is modeled by massive Dirac theory. As a representative example of the formulation presented here, we obtain closed form formula for the third harmonic generation (THG) in gapped graphene. It turns out that the covariant form of the low-energy theory gives rise to a peculiar logarithmic singularities in the nonlinear optical spectra. The universal functional dependence of the response function on dimension-less quantities indicates that the optical nonlinearity can be largely enhanced by tuning the gap to smaller values.