Topological insulators with perfect vacancy superstructure and possible implications for iron chalcogenide superconductors

TL;DR

This paper models topological insulators with vacancy superstructures on a square lattice, revealing tunable topological phases that could explain properties of iron chalcogenide superconductors.

Contribution

It introduces a single orbital tight-binding model with vacancy superstructure capturing topological phases relevant to iron chalcogenide superconductors.

Findings

Topological insulator phases are tunable at specific electron fillings.

The vacancy superstructure naturally supports a non-zero Berry phase.

Implications for iron-deficient compounds are discussed.

Abstract

Motivated by the newly-discovered intercalated iron chalcogenide superconductors, we construct a single orbital tight-binding model for topological insulators on the square lattice with a perfect vacancy superstructure. We find that such lattice structure naturally accommodates a non-vanishing geometry phase associated with the next-nearest-neighbor spin-orbit interaction. By calculating the bulk band structures and the finite stripe edge states, we show that the topological insulator phases can be tuned at certain electron fillings in a wide range of the model parameters. The possible implications of these results for the iron deficient compounds $(A,Tl)_{y}Fe_{2-x}Se_2$ have been discussed.