Appearance of superconductivity in layered LaO_0.5F _0.5BiS₂

Phase pure samples of LaOBiS₂ and LaO_0.5F _0.5BiS₂ are synthesized by conventional solid state reaction route via vacuum encapsulation technique at 800 °C for 12 h. Both the samples are crystallized in tetragonal P4/nmm space group with lattice parameters a=4.066(1) Å, c=13.862(4) Å for LaOBiS₂; a=4.069(5) Å, c=13.366(2) Å for LaO_0.5F _0.5BiS₂. Bulk superconductivity is confirmed in LaO _0.5F_0.5BiS₂ with superconducting transition temperature (T_c) of 2.7 K by DC magnetization and resistivity measurements. The isothermal magnetization (M-H) measurement shows closed loops with clear signatures of flux pinning and irreversible behavior. The magneto-transport ρ(T,H) measurements show resistive broadening and decrease in T_c (ρ=0) to the lower temperature with increasing magnetic field. The magnetic phase diagram involving upper critical and irreversibility fields as a function of temperature has been ascertained. The upper critical field H_c2(0) is estimated to be ∼19 kOe corresponding to a Ginzburg-Landau coherence length of ∼130 Å.