Effects of heterostrain and lattice relaxation on optical conductivity of twisted bilayer graphene

TL;DR

This paper theoretically investigates how heterostrain and lattice relaxation influence the optical conductivity of twisted bilayer graphene near the magic angle, revealing distinctive spectroscopic signatures useful for probing these effects.

Contribution

It introduces a continuum model analysis showing how heterostrain and lattice relaxation uniquely modify optical spectra in twisted bilayer graphene.

Findings

Distinctive spectroscopic features due to heterostrain and relaxation.

Optical peaks reveal information about bandgap, bandwidth, and van Hove singularities.

Strain direction significantly affects flat band transition peaks.

Abstract

We present a theoretical study of the effects of heterostrain and lattice relaxation on the optical conductivity of twisted bilayer graphene near the magic angle, based on the band structures obtained from a continuum model. We find that heterostrain, lattice relaxation and their combination give rise to very distinctive spectroscopic features in the optical conductivity, which can be used to probe and distinguish these effects. From the spectrum at various Fermi energies, important features in the strain- and relaxation-modified band structure such as the bandgap, bandwidth and van Hove singularities can be directly measured. The peak associated with the transition between the flat bands in the optical conductivity are highly sensitive to the direction of the strain, which can provide direct information on the strain-modified flat bands.