THz radiation induced circular Hall effect in graphene

TL;DR

This paper reports the discovery of a circular Hall effect in graphene induced by terahertz radiation, revealing new symmetry-breaking phenomena and nonlinear photoconductivity behaviors without magnetic fields.

Contribution

It demonstrates the observation of a helicity-dependent Hall effect in graphene caused by terahertz radiation, highlighting novel nonlinear effects and symmetry-breaking mechanisms.

Findings

Reversal of photoconductivity sign with radiation helicity

Linear response at low gate voltages proportional to radiation intensity

Superlinear and quadratic intensity dependence at high gate voltages

Abstract

We report on the observation of the circular transversal terahertz photoconductivity in monolayer graphene supplied by a back gate. The photoconductivity response is caused by the free carrier absorption and reverses its sign upon switching the radiation helicity. The observed dc Hall effect manifests the time inversion symmetry breaking induced by circularly polarized terahertz radiation in the absence of a magnetic field. For low gate voltages, the photosignal is found to be proportional to the radiation intensity and can be ascribed to the alignment of electron momenta by the combined action of THz and static electric fields as well as by the dynamic heating and cooling of the electron gas. Strikingly, at high gate voltages, we observe that the linear-in-intensity Hall photoconductivity vanishes; the photoresponse at low intensities becomes superlinear and varies with the square of the radiation intensity. We attribute this behavior to the interplay of the second- and fourth-order effects in the radiation electric field which has not been addressed theoretically so far and requires additional studies.