Upper critical field, anisotropy, and superconducting properties of Ba1-xKxFe2As2 single crystals

The temperature-dependent resistivity of Ba1-xKxFe2As2 (x=0.23, 0.25, 0.28, and 0.4) single crystals and the angle-dependent resistivity of superconducting Ba0.6K0.4Fe2As2 single crystals were measured in magnetic fields up to 9 T. The data measured on samples with different doping levels revealed very high upper critical fields, which increase with the transition temperature, and a very low superconducting anisotropy ratio Gamma=H-c2(ab)/H-c2(c)approximate to 2. By scaling the resistivity within the framework of the anisotropic Ginzburg-Landau theory, the angle-dependent resistivity of the Ba0.6K0.4Fe2As2 single crystal measured with different magnetic fields at a certain temperature collapsed onto one curve. As the only scaling parameter, the anisotropy Gamma was alternatively determined for each temperature and was found to be between two and three.