Saddle-point von Hove singularity and dual topological insulator state in Pt${}_2$HgSe${}_3$

Abstract

Saddle-point van Hove singularities in the topological surface states are interesting because they can provide a new pathway for accessing exotic correlated phenomena in topological materials. Here, based on first-principles calculations combined with a $\mathbf{k}\cdot \mathbf{p}$ model Hamiltonian analysis, we show that the layered platinum mineral jacutingaite (Pt${}_2$HgSe${}_3$) harbours saddle-like topological surface states with associated van Hove singularities. Pt${}_2$HgSe${}_3$ is shown to host two distinct types of nodal lines without spin-orbit coupling (SOC) which are protected by combined inversion ($I$) and time-reversal ($T$) symmetries. Switching on the SOC gaps out the nodal lines and drives the system into a topological insulator state with nonzero weak topological invariant $Z_2=(0;001)$ and mirror Chern number $n_M=2$. Surface states on the naturally cleaved (001) surface are found to be nontrivial with a unique saddle-like energy dispersion with type II van Hove singularities. We also discuss how modulating the crystal structure can drive Pt${}_2$HgSe${}_3$ into a Dirac semimetal state with a pair of Dirac points. Our results indicate that Pt${}_2$HgSe${}_3$ is an ideal candidate material for exploring the properties of topological insulators with saddle-like surface states.

Final PRB version