Non-trivial topology in rare-earth monopnictides from dimensionality reduction

TL;DR

This paper demonstrates that thin films of non-magnetic LaSb exhibit a quantum spin Hall insulator phase due to quantum confinement effects, revealing non-trivial topological properties in rare-earth monopnictides.

Contribution

It uncovers the emergence of a quantum spin Hall phase in LaSb thin films caused by dimensionality reduction and quantum confinement effects.

Findings

Quantum spin Hall phase appears in LaSb films of 3-7 monolayers.

Quantum confinement induces band inversion in LaSb thin films.

The effect is likely general in rare-earth monopnictides.

Abstract

Thin films of rare-earth monopnictide semimetals are expected to turn into semiconductors due to quantum confinement effect, which lifts the overlap between electron pockets at Brillouin zone edges and hole pockets at the zone center. Instead, taking non-magnetic LaSb as an example, we find the emergence of a quantum spin Hall insulator phase in LaSb(001) films as the thickness is reduced to 7, 5, or 3 monolayers. This is attributed to a strong quantum confinement effect on the in-plane electron pockets, and the lack of quantum confinement on the out-of-plane pocket in reciprocal space projected onto zone center, leading to a band inversion. Spin-orbit coupling opens a sizeable non-trivial gap in the band structure of the thin films. Such effect is shown to be general in rare-earth monopnictides and may lead to interesting phenomena when coupled with the 4f magnetic moments present in other members of this family of materials.