Resonant Structure of Second Harmonic Generation in Multilayer Graphene Polytypes

TL;DR

This paper investigates how second harmonic generation (SHG) varies with stacking order, environment, and doping in multilayer graphene, proposing SHG as a non-invasive method to identify different graphene polytypes and their crystallographic orientations.

Contribution

It reveals stacking-dependent resonant features in SHG spectra of multilayer graphene, enabling optical identification of polytypes and crystallographic directions.

Findings

SHG spectra show stacking-order-dependent resonances.

Infra-red SHG can distinguish between MLG polytypes.

SHG sensitivity to electron-hole asymmetry and doping.

Abstract

Second harmonic generation (SHG) is a powerful optical tool for identifying non-centrosymmetric crystalline structures. Here, we analyze SHG in multilayer graphenes (MLG), with a focus on its dependence on the stacking order, encapsulation environment and biasing which break inversion symmetry in multilayers, as well as the SHG sensitivity to the electron-hole asymmetry in the MLG spectra and doping. In particular, we identify stacking-order-dependent resonant features in the SHG spectra for trilayers and tetralayers, suggesting that infra-red range SHG offers a non-invasive characterization method for distinguishing between MLG polytypes, as well as optical identification of crystallographic direction in MLG films.