Quantum Hall edge states under periodic driving: a Floquet induced chirality switch

TL;DR

This paper investigates how strong laser illumination affects quantum Hall edge states in graphene, revealing a Floquet-induced control over edge transport and chirality, with potential applications in topological electronics.

Contribution

It demonstrates that laser polarization can switch and reverse the chirality of quantum Hall edge states in graphene using Floquet theory, a novel control mechanism.

Findings

Laser polarization controls Hall conductance near the Dirac point.

Floquet gaps lead to a switch-off of edge transport for certain edge terminations.

Chirality of edge states can be reversed by changing laser polarization.

Abstract

We report on the fate of the quantum Hall effect in graphene under strong laser illumination. By using Floquet theory combined with both a low energy description and full tight-binding models, we clarify the selection rules, the quasienergy band structure, as well as their connection with the two-terminal and multi-terminal conductance in a device setup as relevant for experiments. We show that the well-known dynamical gaps that appear in the Floquet spectrum at $\pm\,\hbar\Omega/2$ lead to a switch-off of the quantum Hall edge transport for different edge terminations except for the armchair one, where two terms cancel out exactly. More interestingly, we show that near the Dirac point changing the laser polarization (circular right or circular left) controls the Hall conductance, by allowing to switch it on or off, or even by flipping its sign, thereby reversing the chirality of the edge states. This might lead to new avenues to fully control topologically protected transport.