Quantized spin pump on helical edge states of a topological insulator

TL;DR

This paper presents a theoretical analysis of a quantized spin pump utilizing helical edge states in a topological insulator, demonstrating controllable, quantized spin and charge transport driven by time-dependent magnetizations.

Contribution

It introduces a novel two-parameter quantum pump model based on topological insulator edge states, revealing quantized spin and charge pumping with controllable polarization and direction.

Findings

Quantized charge and spin can be pumped in a cycle when Fermi energy is in the magnetization-induced gap.

The pump current can be fully spin-polarized, unpolarized, or pure spin current.

The direction of the pumped current can be reversed by tuning system parameters.

Abstract

We report a theoretical study of the quantized spin pump in a traditional two-parameter quantum pump device that is based on the helical edge states of a quantum spin Hall insulator. By introducing two time-dependent magnetizations out of phase as the pumping parameters, we found that when the Fermi energy resides in the energy gap opened by magnetization, an integer number of charges or spins can be pumped out in a pumping cycle and ascribed to the possible topological interface state born in between the two pumping potentials. The quantized pump current can be fully spin-polarized, spin-unpolarized, or pure spin current while its direction can be abruptly reversed by some system parameters such as the pumping phase and local gate voltage. Our findings may shed light on generation of a quantized spin pump.