Josephson vortices and intrinsic Josephson junctions in the layered iron-based superconductor Ca_(10)(Pt_(3)As_(8))((Fe_(0.9)Pt_(0.1))_(2)As_(2))_(5)

摘要

Modulated electronic state due to the layered crystal structures brings about moderate anisotropy of superconductivity in the iron-based superconductors and thus Abrikosov vortices are expected in the mixed state.However,based on the angular and temperature dependent transport measurements in iron-based superconductor Ca_(10)(Pt_(3)As_(8))((Fe_(0.9)Pt_(0.1))_(2)As_(2))_(5) with Tc(≌)12 K,we find clear evidences of a crossover from Abrikosov vortices to Josephson vortices at a crossover temperature T*(≌)7 K,when the applied magnetic field is parallel to the superconducting FeAs layers,i.e.,the angle between the magnetic field and the FeAs layers θ=0°.This crossover to Josephson vortices is demonstrated by an abnormal decrease(increase)of the critical current(flux-flow resistance)below T*,in contrast to the increase(decrease)of the critical current(flux-flow resistance)above T* expected for Abrikosov vortices.Furthermore,when θ is larger than 0.5°,the flux-flow resistance and critical current have no anomalous behaviors across T*.These anomalous behaviors can be understood in terms of the distinct transition from the well-pinned Abrikosov vortices to the weakly-pinned Josephson vortices upon cooling,when the coherent length perpendicular to the FeAs layers ξ⊥ becomes shorter than half of the interlayer distance d/2.These experimental findings indicate the existence of intrinsic Josephson junctions below T* and thus quasi-two-dimensional superconductivity in Ca10(Pt3As8)((Fe0.9Pt0.1)2As2)5,similar to those in the cuprate superconductors.