  High resolution angle-resolved photoemission measurements have been carried
out on transition metal dichalcogenide PdTe2 that is a superconductor with a Tc
at 1.7 K. Combined with theoretical calculations, we have discovered 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 deep 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
deep below the Fermi level provides a unique system to explore for new
phenomena and properties and opens a door for finding new topological materials
in transition metal chalcogenides.
