Optical Hall response of bilayer graphene: the manifestation of chiral hybridised states in broken mirror symmetry lattices

TL;DR

This paper investigates the optical Hall response of bilayer graphene, revealing how chiral hybridized states in broken mirror symmetry lattices lead to polarization deflection and circular dichroism, with implications for nanoscale light manipulation.

Contribution

It introduces an efficient calculation scheme for optical conductivity in bilayer graphene and demonstrates how chiral hybridized states cause Hall conductivity and optical activity.

Findings

Twisted bilayer graphene exhibits circular dichroism.

Chiral hybridized states cause nonzero Hall conductivity.

Optical properties depend continuously on twist angle and sliding vector.

Abstract

Understanding the mechanisms governing the optical activity of layered-stacked materials is crucial to the design of devices aimed at manipulating light at the nanoscale. Here, we show that both twisted and slid bilayer graphene are chiral systems that can deflect the polarization of linear polarized light. However, only twisted bilayer graphene supports circular dichroism. Our calculation scheme, which is based on the time-dependent Schr\"odinger equation, is particularly efficient for calculating the optical-conductivity tensor. Specifically, it allows us to show the chirality of hybridized states as the handedness-dependent bending of the trajectory of kicked Gaussian wave packets in bilayer lattices. We show that nonzero Hall conductivity is the result of the noncanceling manifestation of hybridized states in chiral lattices. We also demonstrate the continuous dependence of the conductivity tensor on the twist angle and the sliding vector.