Identification of Topological Surface State in PdTe2 Superconductor by Angle-Resolved Photoemission Spectroscopy**Supported by the National Natural Science Foundation of China under Grant Nos 11190022, 11274359 and 11422428, the National Basic Research Program of China under Grant Nos 2011CB921703, 2011CBA00110, 2011CBA00108 and 2013CB921700, and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences under Grant Nos XDB07020300 and

Abstract

High-resolution angle-resolved photoemission measurements are carried out on transition metal dichalcogenide PdTe2 that is a superconductor with a Tc 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.