Non-adiabatic topological spin pumping

TL;DR

This paper analytically studies topological spin pumping using Floquet scattering theory, revealing conditions for robustness and decay of spin transport related to the pumping frequency and system's topological properties.

Contribution

It introduces Floquet spin Chern numbers to characterize topological spin pumping in periodically driven systems with an exactly solvable model.

Findings

Topological spin pumping is robust below the band gap frequency.

Spin pumping rate decays rapidly above the band gap frequency.

Floquet spin Chern numbers effectively characterize the topological nature of the system.

Abstract

Based on the Floquet scattering theory, we analytically investigate the topological spin pumping for an exactly solvable model. Floquet spin Chern numbers are introduced to characterize the periodically time-dependent system. The topological spin pumping remains robust both in the presence and in the absence of the time-reversal symmetry, as long as the pumping frequency is smaller than the band gap, where the electron transport involves only the Floquet evanescent modes in the pump. For the pumping frequency greater than the band gap, where the propagating modes in the pump participate in the electron transport, the spin pumping rate decays rapidly, marking the end of the topological pumping regime.