Monolayer Graphene Can Emit SHG Waves

Abstract

The usually-held notion that monolayer graphene, a centrosymmetric system, does not allow even-harmonic generation when illuminated at normal incidence is challenged by the discovery of a peculiar effect we term the dynamical centrosymmetry breaking mechanism. This effect results in a global pulse-induced oscillation of the Dirac cones which in turn produces 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. These results clear the way for further investigation concerning nonlinear light-matter interactions in a wide range of two-dimensional materials admitting either a gapped or ungapped Dirac-like spectrum.