Observation of chiral photocurrent transport in the quantum Hall regime in graphene

TL;DR

This study demonstrates chiral photocurrent transport in graphene's quantum Hall regime, revealing Landau-level quantization effects and the dependence of edge transport chirality on the Fermi level position.

Contribution

It provides the first experimental observation of chiral photocurrent transport in graphene under quantum Hall conditions, linking photocurrent oscillations to Landau levels and edge state chirality.

Findings

Photocurrent oscillates with Fermi level, indicating Landau-level quantization.

Chiral edge transport dominates photocurrent in the quantum Hall regime.

Electron and hole chiralities are the same away from the Dirac point, opposite near it.

Abstract

Optical excitation provides a powerful tool to investigate non-equilibrium physics in quantum Hall systems. Moreover, the length scale associated with photo-excited charge carries lies between that of local probes and global transport measurements. Here, we investigate non-equilibrium physics of optically-excited charge carriers in graphene through photocurrent measurements in the integer quantum Hall regime. We observe that the photocurrent oscillates as a function of Fermi level, revealing the Landau-level quantization, and that the photocurrent oscillations are different for Fermi levels near and distant from the Dirac point. Our observation qualitatively agrees with a model that assumes the photocurrent is dominated by chiral edge transport of non-equilibrium carriers. Our experimental results are consistent with electron and hole chiralities being the same when the Fermi level is distant from the Dirac point, and opposite when near the Dirac point.