Norihito Kijima

Superconductivity and metal-insulator transition in Cu(Ir1−x Rh x )2S4

A new thiospinel CuIr2S4 exhibits a metal-insulator (M-I) transition at 226 K, while CuRh2S4 shows a superconducting transition at 4.70 K. We present a systematic study of electrical and magnetic properties of Cu(Ir1−xRhx)2S4. TheM-I transition of CuIr2S4 is accompanied by a structural phase transition from tetragonal symmetry in insulating phase to cubic symmetry in high temperature metallic phase. With increasing Rh contentx, the sharpM-I transition shifts to lower temperature forx≦0.10. The samples show semiconductive behavior for 0.10≦0.30 between 4.2 and 300 K, and recover the metallic state forx≧0.50. The superconducting transition may occur for very close tox=1.00. Magnetic susceptibility shows the jump at theM-I transition temperature and the variation ofx leads to a systematic change of the magnetic susceptibilities, which is consistent with the electrical characteristic feature.

Superconductivity in CuRh2(S1−xTex)4

Abstract Cubic spinel solid solution system CuRh2(S1−xTex)4 (0 ≦ x ≦ 0.1) has been synthesized by a solid-state reaction technique. Transport and magnetic properties have been studied. The lattice constant, a, increases rapidly for x ≦ 0.02 with increasing Te content and then is not sensitive to x in the range 0.02 ≦ x ≦ 0.1. The superconducting transition temperature, Tc, decreases also abruptly for x ≦ 0.02 then decreases linearly with x. It is found experimentally that there exists a strong correlation between the lattice constant a and the value of Tc. The principal features of the superconductivity could be accounted for in terms of the decrease of the density of state at the Fermi level by Te substitution.

Superconductivity in Li(Ti1−xVx)2O4

Abstract Detailed resistivity and susceptibility measurements are reported on Li(Ti 1− x V x ) 2 O 4 specimens for 0 ≦ x ≦ 0.05. Even low V-doping strongly suppresses the superconductivity. For x = 0.05, the superconductivity is almost smeared out. The localized magnetic moment per V atom is estimated to be about 1.7 μ B which indicates the V 4+ state with S = 1 2 . The localized magnetic moments induced by the V-doping are responsible for the pair breaking and the extreme sensitivity of the superconductivity.

Superconductivity in SrTa2S5

A strontium tantalum sulfide, SrTa2S5, has a hexagonal structure with lattice constants of a =3.32 and c=24.1 Å. With decreasing temperature the electrical resistivity decreases monotonically and exhibits an abrupt superconducting transition at 3.16 K (midpoint). The diamagnetic susceptibility is observed below Tc. The magnetic susceptibility is nearly independent of temperature above Tc and shows Pauli paramagnetism.

Probing giant reduction of Tc in the Li(Ti1−xVx)2O4 spinel system

Abstract The doping effect of Vanadium in polycrystalline LiTi2O4 material is carefully analysed. We report on the detailed electrical and magnetic properties of Li(Ti1−xVx)2O4 system for 0⩽x⩽0.05 with an emphasis on the low Vanadium concentration. We have an interesting finding to report in that the doping of Vanadium in LiTi2O4, leads to a giant Tc reduction. The localized magnetic moments induced by the Vanadium doping seem to be responsible for the reduction in Tc.

Evidence for Superconductivity in RuSb

Measurements of electrical resistivity, magnetic susceptibility and specific heat have been carried out to study superconductivity in RuSb with MnP-type structure using sintered specimens. The superconducting transition takes place at T c of 0.86 K and the resistivity shows a linear temperature dependence above T c . The susceptibility shows perfect diamagnetism below T c and the Pauli paramagnetism above T c . The specific heat exhibits a broad peak at T c . The electronic-specific-heat coefficient γ is 5.5 mJ/(K2 mol-f.u.) and the Debye temperature Θ is 212 K. The electron-phonon coupling constant γ ep is 0.46. RuSb is a weak-coupling superconductor.