Group VIII transition-metal dichalcogenides have recently been proposed to host type-II Dirac fermions. They are Lorentz-violating quasiparticles marked by a strongly tilted conic dispersion along a certain momentum direction and therefore have no analogs in the standard model. Using high-resolution angle-resolved photoemission spectroscopy, we systematically studied the electronic structure of $\mathrm{PtS}{\mathrm{e}}_2$ in the full three-dimensional Brillouin zone. As predicted, a pair of type-II Dirac crossings is experimentally confirmed along the $k_z$ axis. Interestingly, we observed conic surface states around time-reversal-invariant momenta $\overline{\mathrm{\Gamma }}$ and $\overline{M}$ points. The signatures of nontrivial topology are confirmed by the first-principles calculation, which shows an intricate parity inversion of bulk states. Our discoveries not only contribute to a better understanding of topological band structure in $\mathrm{PtS}{\mathrm{e}}_2$ but also help further explore the exotic properties, as well as potential application, of group VIII transition-metal dichalcogenides.

• Received 31 August 2017
• Revised 1 November 2017

DOI:https://doi.org/10.1103/PhysRevMaterials.1.074202