Re-emerging superconductivity at 27 K in the slightly platinum doped nonsuperconducting Ca0.745La0.255FeAs2

Abstract

High-temperature superconductivity (SC) in iron-based superconductors (IBSs) is usually suppressed or disappeared in the electron/hole overdoped region. Here, we report the reemergence of bulk SC with Tc of 27 K in the La overdoped 112-type Ca0.745La0.255FeAs2 (non-SC) by 4% 5d Pt substitution on the Fe site. The superconducting and normal states properties are systematically characterized by the magnetization and electrical transport measurements. The anisotropy of the upper critical field resides in the range 3–7.2 near Tc. Magnetization measurement reveals a relatively large critical current density Jc∼1.8 × 105 A/cm2 at T = 3 K (self-field). Scaling analysis of the vortex pinning force density versus reduced magnetic field suggests that the main pinning sources are normal point-like defects. Moreover, the negative Hall coefficient RH increases monotonically with decreasing temperature. Intriguingly, a nonmonotonic temperature dependence of magnetoresistance below 100 K, possibly of pseudogap effect in origin, is observed, which is reminiscent of the observation in Ba1-xKxFe2As2 system. In addition, the magnetoresistance does not follow Kohler’s law, indicative of either a change of carriers with T or exotic anisotropic scattering, presumably due to the latent magnetic fluctuation or multiband effect. Our results provide more insight into the reemergence of superconductivity in the electron overdoped 112-type IBSs.