Topological characters in Fe(Te1-xSex) thin films

We investigate topological properties in the Fe(Te,Se) thin films. We find that the single layer FeTe1-xSex has nontrivial Z2 topological invariance which originates from the parity exchange at the Γ point of the Brillouin zone. The nontrivial topology is mainly controlled by the Te(Se) height. Adjusting the anion height, which can be realized as the function of lattice constants and x in FeTe1-xSex, can drive a topological phase transition. In a bulk material, the two-dimensional Z2 topology invariance is extended to a strong three-dimensional one. In a thin film, we predict that the topological invariance oscillates with the number of layers. The results can also be applied to iron pnictides. Our research establishes FeTe1-xSex as a unique system to integrate high-Tc superconductivity and topological properties in a single electronic structure.