Chiral transport of hot carriers in graphene in the quantum Hall regime

TL;DR

This study investigates chiral photocurrents in graphene under quantum Hall conditions, revealing oscillations and dependencies on magnetic field and gate voltage, and models these phenomena to understand hot carrier dynamics and potential carrier multiplication.

Contribution

It provides the first accurate measurement of photocurrents in graphene's quantum Hall regime and develops a theoretical model explaining observed oscillations and saturation behaviors.

Findings

Observed prominent photocurrent oscillations with gate voltage.

Photocurrent envelope depends on magnetic field strength.

Model agrees with experimental data, indicating carrier multiplication.

Abstract

Photocurrent (PC) measurements can reveal the relaxation dynamics of photo-excited hot carriers beyond the linear response of conventional transport experiments, a regime important for carrier multiplication. In graphene subject to a magnetic field, PC measurements are able to probe the existence of Landau levels with different edge chiralities which is exclusive to relativistic electron systems. Here, we report the accurate measurement of PC in graphene in the quantum Hall regime. Prominent PC oscillations as a function of gate voltage on samples' edges are observed. These oscillation amplitudes form an envelope which depends on the strength of the magnetic field, as does the PCs' power dependence and their saturation behavior. We explain these experimental observations through a model using optical Bloch equations, incorporating relaxations through acoustic-, optical- phonons and Coulomb interactions. The simulated PC agrees with our experimental results, leading to a unified understanding of the chiral PC in graphene at various magnetic field strengths, and providing hints for the occurrence of a sizable carrier multiplication.