Prediction of dual quantum spin Hall insulator in NbIrTe$_4$ monolayer

TL;DR

This paper predicts a dual quantum spin Hall insulator in NbIrTe4 monolayer, featuring multiple band inversions and a sizable topological gap, offering a platform to study topology and correlation effects.

Contribution

The study predicts a dual QSHI state in NbIrTe4 monolayer with multiple band inversions and larger topological gaps, expanding the class of 2D topological materials.

Findings

Dual QSHI state predicted in NbIrTe4 monolayer.

Two new band inversions found after CDW phase transition.

VHS-induced band gap around 10 meV, larger than in TaIrTe4.

Abstract

Dual quantum spin Hall insulator (QSHI) is a newly discovered topological state in the 2D material TaIrTe$_4$, exhibiting both a traditional $Z_2$ band gap at charge neutrality point and a van Hove singularity (VHS) induced correlated $Z_2$ band gap with weak doping. Inspired by the recent progress in theoretical understanding and experimental measurements, we predicted a promising dual QSHI in the counterpart material of the NbIrTe4 monolayer by first-principles calculations. In addition to the well-known band inversion at the charge neutrality point, two new band inversions were found after CDW phase transition when the chemical potential is near the VHS, one direct and one indirect $Z_2$ band gap. The VHS-induced non-trivial band gap is around 10 meV, much larger than that from TaIrTe$_4$. Furthermore, since the new generated band gap is mainly dominated by the $4d$ orbitals of Nb, electronic correlation effects should be relatively stronger in NbIrTe$_4$ as compared to TaIrTe$_4$. Therefore, the dual QSHI state in the NbIrTe$_4$ monolayer is expected to be a good platform for investigating the interplay between topology and correlation effects.