Hybridization Gap and Edge States in Strained-layer InAs/In0.5Ga0.5Sb Quantum Spin Hall Insulator

TL;DR

This paper demonstrates the growth of highly strained InAs/In0.5Ga0.5Sb quantum wells that maintain topological edge states, showing enhanced hybridization gaps and robustness of the quantum spin Hall phase under significant strain.

Contribution

It introduces a method for growing highly strained InAs/In0.5Ga0.5Sb quantum wells that preserve topological properties, expanding the strain range for QSHI materials.

Findings

Enhanced hybridization gap in strained-layer QSHIs.

Robust topological edge states under high strain.

Giant magnetoresistance observed in edge states.

Abstract

The hybridization gap in strained-layer InAs/InxGa1-xSb quantum spin Hall insulators (QSHIs) is significantly enhanced compared to binary InAs/GaSb QSHI structures, where the typical indium composition, x, ranges between 0.2 and 0.4. This enhancement prompts a critical question: to what extent can quantum wells (QWs) be strained while still preserving the fundamental QSHI phase? In this study, we demonstrate the controlled molecular beam epitaxial (MBE) growth of highly strained-layer QWs with an indium composition of x = 0.5. These structures possess a substantial compressive strain within the In0.5Ga0.5Sb QW. Detailed crystal structure analyses confirm the exceptional quality of the resulting epitaxial films, indicating coherent lattice structures and the absence of visible dislocations. Transport measurements further reveal that the QSHI phase in InAs/In0.5Ga0.5Sb QWs is robust and protected by time-reversal symmetry. Notably, the edge states in these systems exhibit giant magnetoresistance when subjected to a modest perpendicular magnetic field. This behavior is in agreement with the Z2 topological property predicted by the Bernevig-Hughes-Zhang (BHZ) model, confirming the preservation of topologically protected edge transport in the presence of enhanced bulk strain.