Superconducting (Li,Fe)OHFeSe Film of High Quality and High Critical Parameters

A superconducting film of (Li_1-xFe_x)OHFeSe is reported for the first time. The thin film exhibits a small in-plane crystal mosaic of 0.22^\circ, in terms of the full width at half maximum of the x-ray rocking curve, and an excellent out-of-plane orientation by x-ray \varphi -scan. Its bulk superconducting transition temperature T_\rm c of 42.4 K is characterized by both zero electrical resistance and diamagnetization measurements. The upper critical field H_\rm c2 is estimated to be 79.5 T and 443 T for the magnetic field perpendicular and parallel to the ab plane, respectively. Moreover, a large critical current density J_\rm c of a value over 0.5 MA/cm^2 is achieved at \sim 20 K. Such a (Li_1-xFe_x)OHFeSe film is therefore not only important to the fundamental research for understanding the high-T_\rm c mechanism, but also promising in the field of high-T_\rm c superconductivity application, especially in high-performance electronic devices and large scientific facilities such as superconducting accelerator.