Optical manifestations of symmetry breaking in bilayer graphene

TL;DR

This paper proposes a spectroscopic method to identify different broken symmetry states in bilayer graphene by analyzing how absorption lineshape depends on light polarization, distinguishing gapped and nematic phases.

Contribution

It introduces a theoretical approach to differentiate symmetry-broken states in bilayer graphene using polarization-dependent optical absorption spectra.

Findings

Absorption lineshape varies with light polarization in strained or nematic phases.

Method applies to infrared and far-infrared spectral ranges.

Distinguishes between gapped and nematic symmetry-breaking states.

Abstract

We propose a spectroscopic method of identifying broken symmetry states of bilayer graphene. We demonstrate theoretically that, in contrast to gapped states, a strained bilayer crystal or nematic phase of the electronic liquid are distinguishable by the dependence of the lineshape of absorption on the polarization of the light. This property is characteristic for both the infrared and far-infrared spectral ranges, which correspond to the absorption by transitions between low-energy bands and split bands, and transitions between the low-energy valence and conduction bands, respectively.