Engineering quantum spin Hall insulators by strained-layer heterostructures

TL;DR

This paper demonstrates that applying strain to InAs/InGaSb heterostructures enhances their topological and spin properties, making them promising candidates for robust quantum spin Hall insulators with potential spintronics applications.

Contribution

It introduces strained-layer heterostructures as a new approach to realize and tune quantum spin Hall insulators with improved bulk resistivity and spin-orbit effects.

Findings

High bulk resistivity in strained heterostructures

Enhanced Rashba spin-orbit splitting due to strain

Fermi level crossing only one spin branch over a wide density range

Abstract

Quantum spin Hall insulators (QSHIs), also known as two-dimensional topological insulators, have emerged as an unconventional class of quantum states with insulating bulk and conducting edges originating from nontrivial inverted band structures, and have been proposed as a platform for exploring spintronics applications and exotic quasiparticles related to the spin-helical edge modes. Despite theoretical proposals for various materials, however, experimental demonstrations of QSHIs have so far been limited to two systems--HgTe/CdTe and InAs/GaSb--both of which are lattice-matched semiconductor heterostructures. Here we report transport measurements in yet another realization of a band-inverted heterostructure as a QSHI candidate--InAs/In$_{x}$Ga$_{1-x}$Sb with lattice mismatch. We show that the compressive strain in the In$_{x}$Ga$_{1-x}$Sb layer enhances the band overlap and energy gap. Consequently, high bulk resistivity, two orders of magnitude higher than for InAs/GaSb, is obtained deep in the band-inverted regime. The strain also enhances bulk Rashba spin-orbit splitting, leading to an unusual situation where the Fermi level crosses only one spin branch for electronlike and holelike bands over a wide density range. These properties make this system a promising platform for robust QSHIs with unique spin properties and demonstrate strain to be an important ingredient for tuning spin-orbit interaction.