Identification of Topological Surface State in PdTe₂ Superconductor by Angle-Resolved Photoemission Spectroscopy^*

High-resolution angle-resolved photoemission measurements are carried out on transition metal dichalcogenide PdTe₂ that is a superconductor with a T_c at 1.7 K. Combined with theoretical calculations, we discover for the first time the existence of topologically nontrivial surface state with Dirac cone in PbTe₂ superconductor. It is located at the Brillouin zone center and possesses helical spin texture. Distinct from the usual three-dimensional topological insulators where the Dirac cone of the surface state lies at the Fermi level, the Dirac point of the surface state in PdTe₂ lies deeply below the Fermi level at ∼1.75 eV binding energy and is well separated from the bulk states. The identification of topological surface state in PdTe₂ superconductor deeply below the Fermi level provides a unique system to explore new phenomena and properties and opens a door for finding new topological materials in transition metal chalcogenides.