Evolution of superconductivity in BiS2-based superocnductor   LaO0.5F0.5Bi(S1-xSex)2
  We have systematically investigated the crystal structure, magnetic susceptibility, and electrical resistivity of the BiS2-based superconductor LaO0.5F0.5Bi(S1-xSex)2 (x = 0 - 0.7). With expanding lattice volume by Se substitution, bulk superconductivity was induced for x > 0.2, and the highest Tc of 3.8 K was observed in x = 0.5 (LaO0.5F0.5BiSSe). Metallic conductivity was observed for x > 0.3 in the resistivity measurement, whereas semiconducting-like behavior was observed for x < 0.2. The induction of bulk superconductivity by the partial substitution of S by Se in the LaO0.5F0.5BiS2 superconductor should be positively linked to the enhancement of metallic conductivity. 
Takafumi Hiroi, Joe Kajitani, Atsushi Omachi, Osuke Miura and   Yoshikazu Mizuguchi
cond-mat.supr-con cond-mat.str-el