From an atomic layer to the bulk: Low-temperature atomistic structure and ferroelectric and electronic properties of SnTe films

SnTe hosts ferroelectricity that competes with its weak nontrivial band topology: in the high-symmetry rocksalt structure-in which its intrinsic electric dipole is quenched-this material develops metallic surface bands, but in its rhombic ground-state configuration-which hosts a nonzero spontaneous electric dipole-the crystalline symmetry is lowered, and the presence of surface electronic bands is not guaranteed. Here, the type of ferroelectric coupling and the atomistic and electronic structure of SnTe films ranging from 2 to 40 atomic layers (ALs) are examined on freestanding samples, to which atomic layers were gradually added. Four-AL SnTe films are antiferroelectrically coupled, while thicker freestanding SnTe films are ferroelectrically coupled. The electronic band gap reduces its magnitude in going from 2 to 40 ALs, but it does not close due to the rhombic nature of the structure. These results bridge the structure of SnTe films from the monolayer to the bulk.