Topological Characters in Fe(Te$_{1-x}$Se$_x$) thin films

TL;DR

This paper explores the topological properties of Fe(Te,Se) thin films, revealing nontrivial $Z_2$ invariance driven by atomic height adjustments, with implications for superconductivity and topological phases.

Contribution

It demonstrates that Fe(Te,Se) thin films possess tunable topological phases linked to atomic height, extending to three dimensions and oscillating with layer number.

Findings

Single-layer FeTe$_{1-x}$Se$_x$ has nontrivial $Z_2$ topological invariance.

Topological phase transition driven by Te(Se) height adjustment.

Topological invariance oscillates with the number of layers in thin films.

Abstract

We investigate topological properties in the Fe(Te,Se) thin films. We find that the single layer FeTe$_{1-x}$Se$_x$ has nontrivial $Z_2$ topological invariance which originates from the parity exchange at $\Gamma$ point of Brillouin zone. The nontrivial topology is mainly controlled by the Te(Se) height. Adjusting the height, which can be realized as function of $x$ in FeTe$_{1-x}$Se$_x$, can drive a topological phase transition. In a bulk material, the two dimensional $Z_2$ 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 FeTe$_{1-x}$Se$_x$ as a unique system to integrate high T$_c$ superconductivity and topological properties in a single electronic structure.