Two-step structural modulations and Fermi liquid state in spinel compound CuV₂S₄

We have studied the magnetic, transport and structural properties of chalcogenide spinel compound CuV₂S₄ using a high-quality polycrystalline sample, in order to clarify the intrinsic physical properties of CuV₂S₄. The magnetic susceptibility and the electrical resistivity exhibit two sharp anomalies. One is reversible for temperature T_t1 = 91.5 K and the other shows a thermal hysteresis of about 4 K at T_t2 = 56 K. We clearly observed for the first time that both anomalies are accompanied with two-step structural modulations. The crystal structure changes the symmetry form cubic to tetragonal at T_t1, and then the lattice constant is modulated discontinuously at T_t2 without changing the symmetry. In addition, the paramagnetic susceptibility is very large, and the electrical resistivity at low temperatures shows a quadratic temperature dependence with the coefficient A = 0.05 μΩ cm/K ², which is larger than that of conventional metals. These results indicate that CuV₂S₄ exhibits a Fermi-liquid-like behavior with strongly correlated electrons at lower temperatures.