Band gap anomaly and topological properties in lead chalcogenides

TL;DR

This study investigates the band gap anomaly in lead chalcogenides using ab initio and tight-binding methods, revealing the topological crystalline insulator nature of PbPo through band inversion and topological invariants.

Contribution

It combines ab initio and tight-binding calculations to explain the band gap anomaly and identifies PbPo as a topological crystalline insulator with specific topological properties.

Findings

PbTe's band gap anomaly linked to Te 5s orbital energy and s-p hopping

PbPo is an indirect band gap semiconductor with band inversion

PbPo is confirmed as a topological crystalline insulator

Abstract

Band gap anomaly is a well-known issue in lead chalcogenides PbX (X=S, Se, Te, Po). Combining ab initio calculations and tight-binding (TB) method, we have studied the band evolution in PbX, and found that the band gap anomaly in PbTe is mainly related to the high onsite energy of Te 5s orbital and the large s-p hopping originated from the irregular extended distribution of Te 5s electrons. Furthermore, our calculations show that PbPo is an indirect band gap (6.5 meV) semiconductor with band inversion at L point, which clearly indicates that PbPo is a topological crystalline insulator (TCI). The calculated mirror Chern number and surface states double confirm this conclusion.