Photoemission spectroscopy of spinel-type CuV ₂S ₄ single crystal

We have performed photoemission spectroscopy studies of single-crystalline CUV ₂S ₄ using synchrotron radiation, in order to clarify the electronic structure changes across the charge density wave (CDW) transitions in a spinel type compound. Photo-energy-dependent studies show a peak structure just below the Fermi level (E _F), which undergoes resonant enhancement at an excitation energy hv = 54.5 eV. This energy corresponds to the V 3p-3d threshold energy, thus suggesting that the density of states (DOS) at E _F is mainly composed of V 3d states. From temperature-dependent measurements, we observe a reduction in spectral DOS at and near E _F, leading to the formation of a pseudogap across CDW transition temperatures. The pseudogap energy scale of ̃0.05 eV, identified at the top of the valence band, is significantly larger than the value expected from a BCS-like transition.