Electric tuning of topological properties in a symmetric broken gap quantum well

A mainstream within topological insulators, GaSb/InAs quantum wells (QWs) present a broken gap alignment for the energy bands which supports the quantum spin Hall insulator phase [1,2] and forms an important building block in the search of exotic states of matter [3]. Such QWs have electrons and holes are confined in different layers, leading to a wide range of possibilities to tune the topological properties. In this work, we study the inverted band structure of a symmetric GaSb/InAs QWs under the influence of an electric field applied along the growth direction, using the 8-band k.p model and the envelope function approximation. Without external fields, the collapse of the energy gap occurs in ~10 nm for the InAs layer (where the conduction and valence states become degenerate) and the application of an electric field reopens the gap with an inverted band structure. The behavior of the hybridization gap and of the corresponding edge states are investigated considering a gradual increasing of the electric field modulus, which shows that they can be externally tuned in this system.
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[2] I. Knez, R.-R. Du and G. Sullivan, Phys. Rev. Lett. 107, 136603 (2011).
[3] V. S. Pribiag et al., Nat. Nanotechnol. 10, 593 (2015).