A computational study of two-terminal transport of Floquet quantum Hall insulators

TL;DR

This paper investigates how periodic driving in quantum Hall insulators can produce robust, high-conductance edge states with large Chern numbers, using Floquet-Green's functions and analyzing their robustness and effects of lead bandwidth.

Contribution

It demonstrates quantized conductance up to 8e^2/h in Floquet topological phases and analyzes robustness of edge states against disorder and lead bandwidth effects.

Findings

Quantized conductance up to 8e^2/h achieved with Floquet sum rule.

Co-propagating edge modes are more robust than counter-propagating ones.

Finite lead bandwidths can affect conductance quantization.

Abstract

Periodic driving fields can induce topological phase transitions, resulting in Floquet topological phases with intriguing properties such as very large Chern numbers and unusual edge states. Whether such Floquet topological phases could generate robust edge state conductance much larger than their static counterparts is an interesting question. In this paper, working under the Keldysh formalism, we study two-lead transport via the edge states of irradiated quantum Hall insulators using the method of recursive Floquet-Green's functions. Focusing on a harmonically-driven Hofstadter model, we show that quantized Hall conductance as large as $8e^2/h$ can be realized, but only after applying the so-called Floquet sum rule. To assess the robustness of edge state transport, we analyze the DC conductance, time-averaged current profile and local density of states. It is found that co-propagating chiral edge modes are more robust against disorder and defects as compared with the remarkable counter-propagating edge modes, as well as certain symmetry-restricted Floquet edge modes. Furthermore, we go beyond the wide-band limit, which is often assumed for the leads, to study how the conductance quantization (after applying the Floquet sum rule) of Floquet edge states can be affected if the leads have finite bandwidths. These results may be useful for the design of transport devices based on Floquet topological matter.