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

Abstract

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 hysteresis in the current-voltage curves and modulation of the critical current by the in-plane magnetic fields. The variation of the critical currents for different magnetic-field directions gave an anisotropy ratio of gamma similar to 5. This three-dimensional electronic structure of our iron pnictide superconductors is in clear contrast to the two-dimensional one observed in cuprate superconductors, another stacked superconducting system.