Dynamical centrosymmetry breaking in graphene

TL;DR

This paper reports the discovery of dynamical centrosymmetry breaking in graphene under intense pulsed illumination, leading to second harmonic generation, and highlights the importance of using the full Dirac equation for accurate modeling.

Contribution

It demonstrates that the full Dirac equation reveals phenomena missed by semiconductor Bloch equations, specifically dynamical symmetry breaking and second harmonic generation in graphene.

Findings

Dynamical centrosymmetry breaking occurs in graphene under intense pulses.

Second harmonic generation is observed due to this symmetry breaking.

Full Dirac equation is necessary to accurately describe these effects.

Abstract

We discover an unusual phenomenon that occurs when a graphene monolayer is illuminated by a short and intense pulse at normal incidence. Due to the pulse-induced oscillations of the Dirac cones, a dynamical breaking of the layer's centrosymmetry takes place, leading to the generation of second harmonic waves. We prove that this result can only be found by using the full Dirac equation and show that the widely used semiconductor Bloch equations fail to reproduce this and some other important physics of graphene. Our results open new windows in the understanding of nonlinear light-matter interactions in a wide variety of new 2D materials with a gapped or ungapped Dirac-like dispersion.