Irradiated bilayer graphene

Abstract

We describe the gated bilayer graphene system when it is subjected to intense terahertzfrequency electromagnetic radiation. We examine the electron band structure and densityof states via exact diagonalization methods within Floquet theory. We find that dynamicalstates are induced which lead to modification of the band structure. We first examinethe situation where there is no external magnetic field. In the unbiased case,dynamical gaps appear in the spectrum which manifest as dips in the densityof states. For finite inter-layer bias (where a static gap is present in the bandstructure of unirradiated bilayer graphene), dynamical states may be induced in thestatic gap. These states can show a high degree of valley polarization. Whenthe system is placed in a strong magnetic field, the radiation induces couplingbetween 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.