Inversion symmetry breaking induced triply degenerate points in orderly arranged PtSeTe family materials

TL;DR

This paper predicts that breaking inversion symmetry in PtSe$_2$ family materials induces a topological transition from Dirac fermions to triply degenerate points (TDPs), revealing new topological phases in these materials.

Contribution

The study demonstrates, through symmetry analysis and first-principles calculations, that inversion symmetry breaking in PtSe$_2$ materials leads to the formation of TDPs, a novel topological transition.

Findings

Inversion symmetry breaking causes Dirac points to split into TDPs.

PtSeTe family materials exhibit topological transitions with TDPs.

Proposed experimental methods to realize ordered PtSeTe materials.

Abstract

$k$ paths exactly with $C_{3v}$ symmetry allow to find triply degenerate points (TDPs) in band structures. The paths that host the type-II Dirac points in PtSe$_2$ family materials also have the $C_{3v}$ spatial symmetry. However, due to Kramers degeneracy (the systems have both inversion symmetry and time reversal symmetry), the crossing points in them are Dirac ones. In this work, based on symmetry analysis, first-principles calculations, and $k\cdot p$ method, we predict that PtSe$_2$ family materials should undergo topological transitions if the inversion symmetry is broken, \emph{i.e.} the Dirac fermions in PtSe$_2$ family materials split into TDPs in PtSeTe family materials (PtSSe, PtSeTe, and PdSeTe) with orderly arranged S/Se (Se/Te). It is different from the case in high-energy physics that breaking inversion symmetry $I$ leads to the splitting of Dirac fermion into Weyl fermions. We also address a possible method to achieve the orderly arranged in PtSeTe family materials in experiments. Our study provides a real example that Dirac points transform into TDPs, and is helpful to investigate the topological transition between Dirac fermions and TDP fermions.