Two different topological insulator phases in NaBaBi

TL;DR

This paper predicts two distinct topological insulator phases in NaBaBi, each with unique spin textures, induced by different band inversions, using ab initio calculations, and highlights NaBaBi as a prototype for materials with variable spin textures.

Contribution

It demonstrates the realization of two different TI phases in NaBaBi with opposite spin textures, expanding understanding of topological phases in materials with multiple band inversions.

Findings

Two TI phases with opposite spin textures identified in NaBaBi.

Band inversion between Bi p and Na s, and Bi p and Ba d bands causes the phases.

NaBaBi can exhibit correlation effects due to d states.

Abstract

By breaking the inversion symmetry of the three-dimensional Dirac metal Na$_3$Bi, we realize topological insulator (TI) phases in the known compound NaBaBi using $ab~initio$ calculations. Two distinct TI phases emerge: one phase is due to band inversion between the Bi $p$ and Na $s$ bands, and the other phase (under pressure) is induced by inversion of the Bi $p$ and Ba $d$ bands. Both phases exhibit Dirac-cone-type surface states, but they have opposite spin textures. In the upper cone, a left-handed spin texture exists for the $s$-$p$ inverted phase (similar to a common TI, e.g., Bi$_2$Se$_3$), whereas a right-handed spin texture appears for the $p$-$d$ inverted phase. NaBaBi presents a prototype model of a TI that exhibits different spin textures in the same material. In addition, NaBaBi may exhibit the introduction of correlation effects to the topological state owing to the existence of $d$ states in the band inversion.