Charge and spin edge currents in two-dimensional Floquet topological superconductors

TL;DR

This paper investigates how periodic driving affects charge and spin edge currents in two-dimensional topological superconductors, revealing induced currents, sign reversals, and robustness of edge states under various conditions.

Contribution

It introduces a detailed analysis of Floquet topological superconductors under periodic perturbations, highlighting the behavior of edge currents and states in trivial and nontrivial phases.

Findings

Edge currents are induced in trivial phases and enhanced in topological phases.

Periodic driving can cause sign reversal of edge currents.

Edge states at finite quasi-energy are generally robust, zero quasi-energy states' stability varies.

Abstract

A time periodic driving on a topologically trivial system induces edge modes and topological properties. In this work we consider triplet and singlet superconductors subject to periodic variations of the chemical potential, spin-orbit coupling and magnetization, in both topologically trivial and nontrivial phases, and study their influence on the charge and spin currents that propagate along the edges of the two-dimensional system, for moderate to large driving frequencies. Currents associated with the edge modes are induced in the trivial phases and enhanced in the topological phases. In some cases there is a sign reversal of the currents as a consequence of the periodic driving. The edge states associated with the finite quasi-energy states at the edge of the Floquet zone are in general robust, while the stability of the zero quasi-energy states depends on the parameters. Also, the spin polarization of the Floquet spectrum quasi-energies is strong as for the unperturbed topological phases. It is found that in some cases the unperturbed edge states are immersed in a continuum of states due to the perturbation, particularly if the driving frequency is not large enough. However, their contribution to the edge currents and spin polarization is still significant.