Upper critical field, critical current density and activation energy of the new La_1-xSm_xO_0.5F_0.5BiS₂ (x = 0.2, 0.8) superconductors

Critical current density (J_c), thermal activation energy (U₀), and upper critical field (H_c2) of La_1-xSm_xO_0.5F_0.5BiS₂ (x = 0.2, 0.8) superconductors are investigated from magnetic field dependent ρ(T) studies. The estimated upper critical field (H_c2) has low values of 1.04 T for x = 0.2 and 1.41 T for x = 0.8. These values are lower than Sm free LaO_0.5F_0.5BiS₂ superconductor (1.9 T). The critical current density (J_c) is estimated to be 1.35 × 10⁵ and 5.07 × 10⁵ A/cm² (2 K) for x = 0.2 and 0.8 respectively, using the Bean's model. The thermal activation energy (U₀/k_B) is 61 K for x = 0.2 and 140 K for x = 0.8 as calculated from Arrhenius plots at low magnetic field (1 T) and indicates a strong flux pinning potential which might be co-existing with applied magnetic field. (author)