Engineering quantum spin Hall insulators by strained-layer heterostructures

Quantum spin Hallinsulators (QSHIs), also known as two-dimensional topologicalinsulators, 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 semiconductorheterostructures. Here, we report transport measurements in yet another realization of a band-invertedheterostructure as a QSHI candidate —InAs/InxGa1 −xSb with lattice mismatch. We show that the compressive strain in the InxGa1 −xSb layer enhances the band overlap andenergy gap. Consequently, high bulkresistivity, 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 the strain to be an important ingredient for tuning spin-orbit interaction.

Source: Applied Physics Letters - November 9, 2016 Category: Physics Authors: T. Akiho, F. Cou ëdo, H. Irie, K. Suzuki, K. Onomitsu and K. Muraki Source Type: research