Superconductivity of Electron-Doped NdOBiS2 by Substitution of Mixed-Valence Ce Ions

Abstract

Superconductivity is achieved in Nd1-xCexOBiS2 via electron doping using mixed-valence Ce ions. Single crystals with x = 0.2, 0.3, 0.4, and 0.5 are generated using a CsCl flux method. Plate-like single crystals with dimensions of 0.8 0.8 0.2 mm3 were obtained. The magnetic susceptibility chi(T) indicates large diamagnetism, and the electrical resistivity rho(T) indicates zero resistivity. The maximum value of Tc is observed at 4.7 K in Nd0.8Ce0.2OBiS2 from chi(T). From the rho(T) measurements taken in several magnetic fields, the upper critical field mu0Hc2(0) is estimated to be about 12 and 0.34 T for the ab- and c-planes, respectively. We redetermined mu0Hc2(0) of NdO0.7F0.3BiS2, as about 35 and 0.78 T for the ab- and c-planes, respectively. The anisotropic parameter is estimated to be about 35 for Nd0.7Ce0.3OBiS2 and 45 for NdO0.7F0.3BiS2. The mu0Hc2(0) of Nd0.7Ce0.3OBiS2 is approximately two times smaller than that of NdO0.7F0.3BiS2, although the difference of Gamma is approximately 10.