Pressure effects on crystal and electronic structure of bismuth tellurohalides

TL;DR

This study explores how applying pressure can induce topological phase transitions in bismuth tellurohalides, revealing a narrow Weyl semimetal phase in BiTeI and the absence of such transitions in BiTeBr and BiTeCl.

Contribution

The paper demonstrates pressure-induced topological transitions in BiTeI and analyzes why similar transitions do not occur in BiTeBr and BiTeCl, using density functional theory and tight-binding methods.

Findings

BiTeI undergoes a transition to a Weyl semimetal and then a topological insulator under pressure.

The Weyl semimetal phase exists in a narrow 0.2 GPa pressure window.

BiTeBr and BiTeCl do not exhibit topological phase transitions up to 18 GPa.

Abstract

We study the possibility of pressure-induced transitions from a normal semiconductor to a topological insulator (TI) in bismuth tellurohalides using density functional theory and tight-binding method. In BiTeI this transition is realized through the formation of an intermediate phase, a Weyl semimetal, that leads to modification of surface state dispersions. In the topologically trivial phase, the surface states exhibit a Bychkov-Rashba type dispersion. The Weyl semimetal phase exists in a narrow pressure interval of 0.2 GPa. After the Weyl semimetal--TI transition occurs, the surface electronic structure is characterized by gapless states with linear dispersion. The peculiarities of the surface states modification under pressure depend on the band-bending effect. We have also calculated the frequencies of Raman active modes for BiTeI in the proposed high-pressure crystal phases in order to compare them with available experimental data. Unlike BiTeI, in BiTeBr and BiTeCl the topological phase transition does not occur. In BiTeBr, the crystal structure changes with pressure but the phase remains a trivial one. However, the transition appears to be possible if the low-pressure crystal structure is retained. In BiTeCl under pressure, the topological phase does not appear up to 18 GPa due to a relatively large band gap width in this compound.