Interplay between spin-orbit interactions and a time-dependent electromagnetic field in monolayer graphene

TL;DR

This paper investigates how circularly and linearly polarized terahertz fields influence spin-orbit interactions in monolayer graphene, revealing controllable energy gaps and dynamic spin and orbital behaviors.

Contribution

It demonstrates how external electromagnetic fields can modulate spin-orbit effects and optical conductivity in graphene, introducing new ways to control its electronic properties.

Findings

Field induces and closes energy gaps depending on polarization.

Spin-orbit coupling signatures appear in density of states at specific energies.

Optical conductivity exhibits multiple steps modifiable by spin-orbit parameters.

Abstract

We apply a circularly and linearly polarized terahertz field on a monolayer of graphene taking into account spin-orbit interactions of the intrinsic and Rashba type. It turns out that the field can not only be used to induce a gap in the energy spectrum, but also to close an existing gap due to the different reaction of the spin components on circularly polarized light. Signatures of spin-orbit coupling on the density of states of the driven system can be observed even for energies where the static density of states is independent of spin-orbit interactions. Furthermore it is shown that the time evolution of the spin polarization and the orbital dynamics of an initial wave packet can be modulated by varying the ratio of the spin-orbit coupling parameters. Assuming that the system acquires a quasi stationary state, the optical conductivity of the irradiated sample is calculated. Our results confirm the multi step nature of the conductivity obtained recently, where the number of intermediate steps can be changed by adjusting the spin-orbit coupling parameters and the orientation of the field.