Photoemission Spectroscopy of Spinel-Type CuV₂S₄ Single Crystal

Abstract

We have performed photoemission spectroscopy studies of single-crystalline CuV₂S₄ 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 hν=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.