Strain-driven onset of nontrivial topological insulating states in Zintl Sr2X compounds (X = Pb, Sn)

We explore the topological behavior of the binary Zintl phase of the alkaline-earth-metal-based compounds Sr2Pb and Sr2Sn using both standard and hybrid density functional theory. It is found that Sr2Pb 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 nontrivial topologically insulating state displays well-defined metallic states in the Sr2Pb(010) surface, whose evolution is studied as a function of the film thickness.