PbTe/PbSnTe heterostructures as analogs of topological insulators

TL;DR

This paper theoretically studies PbTe/PbSnTe heterostructures grown along [111], revealing conditions under which helical Dirac fermions emerge at interfaces, resembling topological insulator surface states, with potential for exploring 2D topological physics.

Contribution

It demonstrates that in PbTe/PbSnTe heterostructures, interface states can remain gapless and helical, akin to topological insulators, under specific thickness and composition conditions.

Findings

Oblique valley states become gapped at d ≈ 10 nm

[111] valley states remain gapless and helical

Potential to study 2D helical Dirac fermions

Abstract

We investigate theoretically the PbTe/PbSnTe heterostructure grown in [111] direction, specifically a quantum wall (potential step of width d) of PbTe embedded in Pb_{1-x}Sn_{x}Te. For x large enough to lead to band inversion, and for large d, there are well-known gapless interface states associated with four L valleys. We show that for d \approx\ 10 nm the three pairs of states from oblique valleys strongly couple, and become gapped with a gap ~10 meV. On the other hand, the interface states from the [111] valley are essentially uncoupled, and they retain their helical character, remaining analogous to states at surfaces of thin layers of three-dimensional topological insulators. This opens up a possibility of studying the physics of two-dimensional helical Dirac fermions in heterostuctures of already widely studied IV-VI semicondcutors.