Strain driven onset of non-trivial topological insulating states in Zintl Sr$_2X$ compounds ($X$=Pb, Sn)

TL;DR

This study investigates how strain can induce topological insulating states in Sr$_2$Pb and Sr$_2$Sn compounds, revealing that a small uniaxial expansion can turn Sr$_2$Pb into a non-trivial topological insulator with metallic surface states.

Contribution

It demonstrates that strain can drive Sr$_2$Pb into a topologically non-trivial phase, providing insights into strain engineering of topological materials.

Findings

Sr$_2$Pb is near a topological instability.

A small uniaxial strain (>3%) induces a topological phase transition.

Surface states evolve with film thickness.

Abstract

We explore the topological behavior of the binary Zintl phase of the alkaline earth metals based compounds Sr$_2$Pb and Sr$_2$Sn using both standard and hybrid density functional theory. It is found that Sr$_2$Pb lies on the verge of a topological instability which can be suitably tuned through the application of a small uniaxial expansion strain ($>$ 3%). The resulting non-trivial topologically insulating state display well-defined metallic states in the Sr$_{2}$Pb(010) surface, whose evolution is studied as a function of the film thickness.