Surface corrugations influence on monolayer graphene electromagnetic response

TL;DR

This paper investigates how surface corrugations in monolayer graphene affect its electromagnetic response in the terahertz range, revealing the influence of local curvature and valley-dependent currents on the induced total current.

Contribution

It introduces a quantum mechanical model accounting for surface corrugations and valley effects to describe the induced current in graphene under terahertz irradiation.

Findings

Surface corrugations alter the local direction of induced currents.

Valley currents exhibit nonzero elliptic polarization and rotate oppositely.

The derived formula describes curved current lines in the linear response regime.

Abstract

We consider the corrugated monolayer graphene membrane electromagnetic (from both valleys) response in terahertz range. We study the generated in irradiated graphene total current for the first time taking into account both the synthetic electric fields arising due to the (inevitable) presence in graphene of inherent out-of-plane nanodeformations and the double-valleys energy spectrum of Dirac charge particles. Our approach is based on atomistic quantum mechanics used for the description of valence ${\pi}-{\sigma}$ bonds changes generated by activating external periodic electric field and also for mechanism of Dirac electron interaction with this time-dependent perturbation. We consider the problem in the framework of the model of noninteracting Dirac electrons. Assuming surface corrugations not to be very rough we obtain for weak fields the formula for the total current induced in graphene membrane. Our formula describes the curved current lines in the linear in $E^{ext}(t)$ approximation for the given graphene surface form. We show that the local direction of current lines is determined by synthetic electric field whose direction may essentially differ from the one of the external field and depends on the local curvature of the graphene membrane. We also demonstrate that valley currents generated by the external field have nonzero elliptic polarization angles depending on the point (x,y). Valley currents are shown to rotate in opposite directions in different valleys. The results obtained below can be applied to the analysis of different devices in terahertz optics and optoelectronics and the imaging experiments at the Dirac point.