Helicity-dependent photocurrents in graphene layers excited by mid-infrared radiation of a CO$_2$-laser

TL;DR

This study investigates helicity-dependent photocurrents in graphene excited by mid-infrared CO2 laser radiation, revealing a resonance linked to SiC phonons and demonstrating effects like the circular $ac$ Hall and photogalvanic effects.

Contribution

It demonstrates the generation of helicity-dependent photocurrents in graphene using mid-infrared radiation and identifies a resonance related to SiC phonons, combining experimental observations with physical effect analysis.

Findings

Photocurrent reverses sign with radiation helicity.

Resonance observed at frequencies matching SiC optical phonons.

Current caused by interplay of circular $ac$ Hall and photogalvanic effects.

Abstract

We report the study of the helicity driven photocurrents in graphene excited by mid-infrared light of a CO$_2$-laser. Illuminating an unbiased monolayer sheet of graphene with circularly polarized radiation generates -- under oblique incidence -- an electric current perpendicular to the plane of incidence, whose sign is reversed by switching the radiation helicity. We show that the current is caused by the interplay of the circular $ac$ Hall effect and the circular photogalvanic effect. Studying the frequency dependence of the current in graphene layers grown on the SiC substrate we observe that the current exhibits a resonance at frequencies matching the longitudinal optical phonon in SiC.