Robust midgap states in band-inverted junctions under electric and magnetic fields

TL;DR

This paper investigates the robustness of midgap topological interface states in band-inverted semiconductor junctions under strong electric and magnetic fields, revealing their persistence and tunability for potential device applications.

Contribution

It provides a comprehensive analysis of how crossed electric and magnetic fields affect topological interface states in band-inverted junctions, demonstrating their robustness and controllability.

Findings

Dirac cone interface states are robust under strong fields.

Electric fields can tune Landau levels in the semiconductor bands.

Topological states persist despite applied electric and magnetic fields.

Abstract

Several IV-VI semiconductor compounds made of heavy atoms, such as Pb$_{1-x}$Sn$_{x}$Te, may undergo band-inversion at the $L$ point of the Brillouin zone upon variation of their chemical composition. This inversion gives rise to topologically distinct phases, characterized by a change in a topological invariant. In the framework of the $\mathbf{k}\cdot\mathbf{p}$ theory, band-inversion can be viewed as a change of sign of the fundamental gap. A two-band model within the envelope-function approximation predicts the appearance of midgap interface states with Dirac cone dispersions in band-inverted junctions, namely, when the gap changes sign along the growth direction. We present a thorough study of these interface electron states in the presence of crossed electric and magnetic fields, the electric field being applied along the growth direction of a band-inverted junction. We show that the Dirac cone is robust and persists even if the fields are strong. In addition, we point out that Landau levels of electron states lying in the semiconductor bands can be tailored by the electric field. Tunable devices are thus likely to be realizable exploiting the properties studied herein.