Irradiated bilayer graphene

TL;DR

This paper investigates how intense terahertz radiation affects the electronic properties of bilayer graphene, revealing dynamical gaps, valley polarization, and Landau level coupling through Floquet theory analysis.

Contribution

It introduces a detailed analysis of irradiated bilayer graphene's band structure using Floquet theory, highlighting the emergence of dynamical states and gaps under various conditions.

Findings

Dynamical gaps appear as dips in the density of states without magnetic field.

Dynamical states can exist within static gaps at finite interlayer bias.

Radiation induces coupling between Landau levels, smearing them into a continuum.

Abstract

We describe the gated bilayer graphene system when it is subjected to intense terahertz frequency electromagnetic radiation. We examine the electron band structure and density of states via exact diagonalization methods within Floquet theory. We find that dynamical states are induced which lead to modification of the band structure. We first examine the situation where there is no external magnetic field. In the unbiased case, dynamical gaps appear in the spectrum which manifest as dips in the density of states. For finite interlayer bias (where a static gap is present in the band structure of unirradiated bilayer graphene), dynamical states may be induced in the static gap. These states can show a high degree of valley polarization. When the system is placed in a strong magnetic field, the radiation induces coupling between the Landau levels which allows dynamical levels to exist. For strong fields, this means the Landau levels are smeared to form a near-continuum of states.