Optical Hall conductivity of a Floquet Topological Insulator

TL;DR

This paper investigates the optical Hall conductivity of Floquet topological insulators in both closed and open quantum systems, revealing how topological phases and system-reservoir interactions influence conductivity and temperature dependence.

Contribution

It provides new insights into the nonequilibrium steady-state behavior of Floquet topological insulators and how their optical Hall conductivity is affected by topological phase and system-reservoir coupling.

Findings

Certain topological phases show near-cancellation of Hall conductivity due to Berry curvature pockets.

The low-frequency Hall conductivity can be suppressed and exhibits anomalous temperature dependence.

Frequency components of time-dependent Berry curvature influence high-frequency Hall conductivity.

Abstract

Results are presented for the optical Hall conductivity of a Floquet topological insulator (FTI) for an ideal closed quantum system, as well as an open system in a nonequilibrium steady-state with a reservoir. The steady-state, even for the open system, is strongly dependent on the topological phase of the FTI, with certain phases showing a remarkable near-cancellation from pockets of Berry-curvature of opposite signs, leading to a suppressed low-frequency Hall conductivity, that also shows an anomalous temperature dependence, by increasing as the temperature of the reservoir is increased. Such a behavior is in complete contrast to heating, and arises because of a strong modification of the effective system-reservoir coupling by the laser. The Berry curvature of the Floquet modes is time-dependent, and its frequency components are found to control the main features of the high-frequency Hall conductivity.