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 k⋅p model Hamiltonian analysis, we show that the layered platinum mineral jacutingaite (Pt2HgSe3) harbours saddle-like topological surface states with associated van Hove singularities. Pt2HgSe3 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 Z2=(0;001) and mirror Chern number nM=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 Pt2HgSe3 into a Dirac semimetal state with a pair of Dirac points. Our results indicate that Pt2HgSe3 is an ideal candidate material for exploring the properties of topological insulators with saddle-like surface states.
@article{arxiv.1905.12578,
title = {Saddle-point von Hove singularity and dual topological insulator state in Pt$_2$HgSe$_3$},
author = {Barun Ghosh and Sougata Mardanya and Bahadur Singh and Xiaoting Zhou and Baokai Wang and Tay-Rong Chang and Chenliang Su and Hsin Lin and Amit Agarwal and Arun Bansil},
journal= {arXiv preprint arXiv:1905.12578},
year = {2020}
}