Superconductivity in Few-layer Stanene*

Superconductivity has been observed in few-layer α-Sn films with thickness down to ~0.72 nm. A BKT-like phase transition behavior as well as distinctly anisotropic upper critical fields have been observed. Furthermore, by varying the thickness of the buffer layer—PbTe(111), thus changing the strain and doping level, we manage to tune the trilayer stanene films from a single-band to a two-band superconductor. This is manifested in the dependence of out-of-plane critical field on critical temperature. A linear response is seen in trilayer stanene grown on 6 layers of PbTe while data points from that on a thicker PbTe demonstrate a concave shape, an archetypical feature of multi-band superconductors. Our in-situ angle-resolved photoemission spectroscopy further reveals that an electron pocket emerges inside the hole band for a trilayer stanene on thicker PbTe substrate. Such an band structure agrees with the theoretically computed energy bands of trilayer stanene in the topological non-trivial phase , indicating that our system could be a topological superconductor.