Photoemission Spectroscopy of Spinel-Type CuV2S4 Single Crystal

We have performed photoemission spectroscopy studies of single-crystalline CuV 2 S 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 h ν= 54.5 eV. This energy corresponds to the V 3 p –3 d threshold energy, thus suggesting that the density of states (DOS) at E F is mainly composed of V 3 d 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.