New Candidates for Topological Insulators : Pb-based chalcogenide series

TL;DR

This paper predicts new Pb-based layered chalcogenides as potential topological insulators, highlighting a large bulk band gap in PbBi$_2$Se$_4$ and tunable topological phases in Pb$_2$Sb$_2$Te$_5$ due to phase boundary proximity.

Contribution

Theoretical prediction of Pb-based layered chalcogenides as new topological insulators with large band gaps and tunable phases.

Findings

PbBi$_2$Se$_4$ has a large 0.40 eV bulk band gap.

Phase transition from topological to band insulator occurs between n=2 and 3.

Pb$_2$Sb$_2$Te$_5$ is near the topological phase boundary, enabling phase tuning.

Abstract

Here, we theoretically predict that the series of Pb-based layered chalcogenides, Pb$_n$Bi$_2$Se$_{n+3}$ and Pb$_n$Sb$_2$Te$_{n+3}$, are possible new candidates for topological insulators. As $n$ increases, the phase transition from a topological insulator to a band insulator is found to occur between $n=2$ and 3 for both series. Significantly, among the new topological insulators, we found a bulk band gap of 0.40eV in PbBi$_2$Se$_4$ which is one of the largest gap topological insulators, and that Pb$_2$Sb$_2$Te$_5$ is located in the immediate vicinity of the topological phase boundary, making its topological phase easily tunable by changing external parameters such as lattice constants. Due to the three-dimensional Dirac cone at the phase boundary, massless Dirac fermions also may be easily accessible in Pb$_2$Sb$_2$Te$_5$.