Josephson vortices and intrinsic Josephson junctions in the layered iron-based superconductor Ca₁₀(Pt₃As₈)((Fe_0.9Pt_0.1)₂As₂)₅

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_3As_8)((Fe_0.9Pt_0.1)_2As_2)_5 with T_\rm c \simeq 12 K, we find clear evidences of a crossover from Abrikosov vortices to Josephson vortices at a crossover temperature T^\star \simeq 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 \theta = 0^\circ. This crossover to Josephson vortices is demonstrated by an abnormal decrease (increase) of the critical current (flux-flow resistance) below T^\star, in contrast to the increase (decrease) of the critical current (flux-flow resistance) above T^\star expected for Abrikosov vortices. Furthermore, when \theta is larger than 0.5^\circ, the flux-flow resistance and critical current have no anomalous behaviors across T^\star. 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 \xi_\bot becomes shorter than half of the interlayer distance d/2. These experimental findings indicate the existence of intrinsic Josephson junctions below T^\star and thus quasi-two-dimensional superconductivity in Ca_10(Pt_3As_8)((Fe_0.9Pt_0.1)_2As_2)_5, similar to those in the cuprate superconductors.