Transport signatures in topological systems coupled to AC fields

TL;DR

This paper investigates how AC electric fields influence transport in topological systems using a non-perturbative Floquet-Keldysh approach, revealing phase changes, side-bands, and zero-energy modes relevant for topological phase detection.

Contribution

It introduces a comprehensive non-perturbative formalism to analyze transport in topological systems under AC fields, covering a wide parameter range and including effects of contact hybridization.

Findings

Hybridization can alter the topological phase.

Current response to field amplitude distinguishes phases.

Presence of Floquet side-bands and zero-energy modes.

Abstract

We study the transport properties of a topological system coupled to an AC electric field by means of Floquet-Keldysh formalism. We consider a semi-infinite chain of dimers coupled to a semi-infinite metallic lead, and obtain the density of states and current when the system is out of equilibrium. Our formalism is non-perturbative and allows us to explore, in the thermodynamic limit, a wide range of regimes for the AC field, arbitrary values of the coupling strength to the metallic contact and corrections to the wide-band limit. We find that hybridization with the contact can change the dimerization phase, and that the current dependence on the field amplitude can be used to discriminate between them. We also show the appearance of side-bands and non-equilibrium zero-energy modes, characteristic of Floquet systems. Our results directly apply to the stability of non-equilibrium topological phases, when transport measurements are used for their detection.