Modulating dichroism and optical conductivity in bilayer graphene under intense electromagnetic field irradiation

TL;DR

This paper investigates how intense electromagnetic fields modify the electronic and optical properties of bilayer graphene, revealing polarization-dependent dichroism and potential for valley-polarized current generation.

Contribution

It introduces a theoretical framework using Floquet-Bloch theory to analyze the effects of strong laser fields on bilayer graphene's band structure and optical conductivity, highlighting polarization-specific phenomena.

Findings

Linear polarization causes anisotropic band dispersion and linear dichroism.

Circular polarization induces Berry curvature and circular dichroism near dynamical gaps.

Circularly polarized light with bias potential leads to valley-polarized currents.

Abstract

This study explores the impact of a strong perpendicular laser field on the electronic structure and optical conductivity of bilayer graphene. Employing the Floquet-Bloch theorem and a four-band Hamiltonian model, we calculate the optical conductivity, unveiling modified optical properties due to the altered band structure. We investigate the effects of both circularly and linearly polarized dressing fields on the electronic structure and optical conductivity in the system. Under linear polarization, we observe a notable anisotropy in the band dispersion and optical conductivity, resulting in linear dichroism. In the case of circular polarization, we anticipate the emergence of induced Berry curvature and circular dichroism, especially close to the dynamical gaps. When circularly polarized light is applied alongside a bias potential, the band structure differs for right-handed and left-handed polarization. In this case, the longitudinal optical conductivity remains the same for both, while the transversal optical conductivity exhibits distinct results. Furthermore, the induced Berry curvature and valley asymmetry introduce the potential for generating a valley-polarized current, enabling valley-selective pumping and leading to circular dichroism.