Enhancement of superconductivity in multilayer FeSe film by Nb coating

Abstract

Recently, the superconductivity of FeSe has been greatly enhanced in one-unit-cell films and ultrathin surface doped films grown on STO substrates, which lead to extensive research on the interfacial effect and charge carriers doping in FeSe films. Herein, by using ion beam sputtering deposition, transition metal (Nb) is successfully coated on the multilayer FeSe films and the superconductivity of FeSe is significantly enhanced compared to pristine FeSe. The superconducting transition temperature (Tc) varies with the thickness of Nb coatings and the highest Tc up to 13.0 K is obtained in the FeSe film with Nb coating about 10 nm. X-ray diffraction analysis (XRD) demonstrates Nb incorporates in FeSe lattice. In particular, the existence of Nb5+ in FeSe films is confirmed by the X-ray photoelectron spectroscopy (XPS). The salient change of Nb binding energy measured by XPS demonstrate the binding and hole-carriers doping mechanisms between Nb5+ and FeSe layers. In particular, the positive Hall coefficients demonstrate the hole carriers dominant in Nb-doped FeSe films. This work demonstrates the doping characteristics of Fe site in FeSe, providing an avenue for exploring diverse superconductivity of FeSe by transition metal doping.