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^o, in terms of the full width at half maximum of X-ray rocking curve, and an excellent out-of-plane orientation by X-ray φ-scan. Its bulk superconducting transition temperature T_c of 42.4 K is characterized by both zero electrical resistance and diamagnetization measurements. The upper critical field H_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_c of a value over 0.5 MA/cm² is achieved at ~20 K. Such a (Li_1-xFe_x)OHFeSe film is therefore not only important to the fundamental research for understanding the high-T_c mechanism, but also promising in the field of high-T_c superconductivity application, especially for high-performance electronic devices and large scientific facilities such as superconducting accelerators.