Enhancement of Superconductivity and Structural Instability by Sn Substitution in LaO_0.5F_0.5BiS₂

Layered BiS₂-based superconductor La(O,F)BiS₂ can exhibit superconductivity via carrier doping, and its superconducting properties can be changed by applying hydrostatic or chemical pressure through elemental substitution. Single-crystal LaO_0.5F_0.5BiS₂ exhibits filamentary superconductivity with T_c of approximately 3 K. We found that the partial substitution of Bi with Sn in LaO_0.5F_0.5BiS₂ induces a structural phase transition from the P4=nmm to P2₁=m structure. Bulk superconductivity with T_c of approximately 6 K emerged near this structural phase transition. We also observed filamentary superconductivity with T_c of approximately 8 K, which was approximately three times higher than that of the unsubstituted sample. This finding provides a new route for further increasing the superconducting transition temperature of this system.