Transport properties and electronic phase diagram of cobalt-doped 1111-type iron arsenide hydride

We successfully synthesized CaHFe1−xCoxAs (0 ≤ x ≤ 0.45) by using a high-pressure and high-temperature solid-state reaction method. By measuring electrical and magnetic properties, we mapped out the phase diagram of the system. The anomaly observed in both resistivity and magnetic susceptibility was continuously suppressed by increasing Co concentration. As doping level increases to 0.07, superconductivity is induced. The maximum superconducting transition temperature Tc = 23.8 K and the full superconductive shielding fraction are observed at the optimal doping level x = 0.15. The superconducting dome in the phase diagram shows a relatively wide and flat shape. The zero-temperature upper critical field Hc2 for an optimally doped sample with x = 0.15 and an overdoped sample with x = 0.3 are 69.3 and 37.7 T, respectively. The temperature dependences of the upper critical fields show upward curvatures, consistent with the multi-band nature of the system.