Superconductivity in La1−xCex OBiSSe: Carrier doping by mixed valence of Ce ions Ryota Sogabe, Yosuke Goto, Atsuhiro Nishida, Takayoshi Katase and Yoshikazu Mizuguchi EPL, 122 1 (2018) 17004 Published online: 05 June 2018 DOI: 10.1209/0295-5075/122/17004