Growth and characterization of R(O,F)BiS2 (R = La, Ce, Pr, Nd) superconducting single crystals

Abstract

R(O,F)BiS2 (R: La, Ce, Pr, Nd) superconducting single crystals with different F concentrations are grown using a CsCl/KCl flux. The obtained 1-2 mm-sized single crystals have a plate-like shape and are cleavable along the ab-plane. The crystal structure is tetragonal of space group P4/nmm (#129). The as-grown single crystals exhibit superconductivity at around 3-5 K. The superconducting transition temperature increases with decreasing the ionic radius of the R element. The superconducting anisotropies of the R(O,F)BiS2 single crystals are estimated to be 30-60 according to the effective mass model, whereas the anisotropies for Ce(O,F)BiS2 single crystals are 13-21. The c-axis transport measurements of a single crystal of Pr(O,F)BiS2 under a magnetic field parallel to the ab-plane reveal a "lock-in" state attributed to the Josephson vortex flow. Furthermore, the Ce(O,F)BiS2 single crystals exhibit a magnetic order at the temperature range of 5-7 K that apparently coexist with superconductivity below approximately 3 K.