Weyl semimetals from noncentrosymmetric topological insulators

TL;DR

This paper demonstrates that Weyl semimetals always appear as an intermediate phase during the transition from 3D topological to normal insulators in noncentrosymmetric materials, supported by first-principles calculations and effective modeling.

Contribution

It proves the universal existence of Weyl semimetals as an intermediate phase in such transitions, regardless of lattice symmetry constraints, and provides specific material examples and models.

Findings

Weyl semimetals appear as an intermediate phase in all studied transitions.

Robust Weyl phases are found in LaBiTe3 and LuBiTe3 solid solutions.

Weyl phase in BiTeI under pressure is very narrow, explaining experimental challenges.

Abstract

We study the problem of phase transitions from 3D topological to normal insulators without inversion symmetry. In contrast with the conclusions of some previous work, we show that a Weyl semimetal always exists as an intermediate phase regardless of any constriant from lattice symmetries, although the interval of the critical region is sensitive to the choice of path in the parameter space and can be very narrow. We demonstrate this behavior by carrying out first-principles calculations on the noncentrosymmetric topological insulators LaBiTe$_3$ and LuBiTe$_3$ and the trivial insulator BiTeI. We find that a robust Weyl-semimetal phase exists in the solid solutions LaBi$_{1-x}$Sb$_x$Te$_3$ and LuBi$_{1-x}$Sb$_x$Te$_3$ for $x\!\approx\!38.5-41.9$\% and $x\!\approx\!40.5-45.1$\% respectively. A low-energy effective model is also constructed to describe the critical behavior in these two materials. In BiTeI, a Weyl semimetal also appears with applied pressure, but only within a very small pressure range, which may explain why it has not been experimentally observed.