Current injection by coherent one- and two-photon excitation in graphene and its bilayer

TL;DR

This paper investigates how coherent optical excitation can inject electrical currents in single and bilayer graphene, revealing unique polarization-dependent effects and signatures of interlayer coupling through theoretical modeling.

Contribution

The study provides a theoretical framework for understanding coherent control of photocurrents in graphene and bilayer graphene, highlighting polarization effects and interlayer coupling signatures.

Findings

Strong photocurrents under co-circular and linear polarizations.

No net current with opposite-circular polarization.

Distinct linear-circular dichroism in two-photon absorption.

Abstract

Coherent control of optically-injected carrier distributions in single and bilayer graphene allows the injection of electrical currents. Using a tight-binding model and Fermi's golden rule, we derive the carrier and photocurrent densities achieved via interference of the quantum amplitudes for two-photon absorption at a fundamental frequency, $\omega$, and one-photon absorption at the second harmonic, $2\omega$. Strong currents are injected under co-circular and linear polarizations. In contrast, opposite-circular polarization yields no net current. For single-layer graphene, the magnitude of the current is unaffected by the rotation of linear-polarization axes, in contrast with the bilayer and with conventional semiconductors. The dependence of the photocurrent on the linear-polarization axes is a clear and measurable signature of interlayer coupling in AB-stacked multilayer graphene. We also find that single and bilayer graphene exhibit a strong, distinct linear-circular dichroism in two-photon absorption.