Absence of Tunneling Character in c-axis Transport of SmFeAsO0.85 Single Crystals

We made electrical transport measurements along the c-axis of SmFeAsO0.85 single crystals, in both three- and four-terminal configurations, focusing on examining the possible formation of Josephson coupling between FeAs superconducting layers. Anisotropic bulk superconductivity was observed along the c-axis, but without Josephson coupling, as confirmed by the absence of both the hysteresis in current-voltage curves and the modulation of the critical current by the in-plane magnetic fields. The variation of the critical currents for different magnetic-field directions gives the anisotropy ratio of 5. This three-dimensional electronic structure of our iron pnictide superconductors is in clear contrast to the two-dimensional one observed in the cuprate superconductors, another stacked superconducting system.