Spin Chern Pumping from the Bulk of Two-Dimensional Topological Insulators

TL;DR

This paper predicts a bulk quantum spin and charge pumping effect in 2D topological insulators, enabling direct measurement of their topological invariants through adiabatic modulation.

Contribution

It introduces a novel bulk quantum pumping mechanism in 2D TIs, linking spin and charge transport to topological invariants via adiabatic cycles.

Findings

Spin can be pumped into electrodes proportional to sample width.

Universal quantized charge conductivities related to spin Chern numbers.

Potential for direct experimental probing of topological properties.

Abstract

Topological insulators (TIs) are a new quantum state of matter discovered recently, which are characterized by unconventional bulk topological invariants. Proposals for practical applications of the TIs are mostly based upon their metallic surface or edge states. Here, we report the theoretical discovery of a bulk quantum pumping effect in a two-dimensional TI electrically modulated in adiabatic cycles. In each cycle, an amount of spin proportional to the sample width can be pumped into a nonmagnetic electrode, which is attributed to nonzero spin Chern numbers $C_{\pm}$. Moreover, by using a half-metallic electrode, universal quantized charge pumping conductivities $-C_{\pm}e^2/h$ can be measured. This discovery paves the way for direct investigation of the robust topological properties of the TIs.