Dirac-like band dispersion at the pyrite-type CuSe2 (100) surface revealed by soft x-ray angle-resolved photoemission spectroscopy

We have investigated the bulk and surface electronic structure of pyrite-type CuSe2 by means of soft x-ray photoemission spectroscopy. The Cu 3d band around 2.5 eV below the Fermi level does not show Cu 2p-3d resonance indicating that the Cu 3d level is almost fully filled and the Cu valence is close to +1. The dispersions of the Cu 3d/Se 4p bands observed by angle-resolved measurements roughly follow slab calculations for (100) surface. The surface of pyrite-type CuSe2 harbors two-dimensional Dirac-like band dispersions at the corner of the surface Brillouin zone suggesting possible interplay between the surface/interface Dirac states and the exotic bulk electronic/lattice properties through the Cu 3d-Se 4p interaction.