Hydrogen exposure-enhanced superconductivity transition in FeSe/SrTiO3 monolayer

Interface-enhanced superconductivity in FeSe/SrTiO3 (FeSe/STO) monolayers provides the record for the highest transition temperature (Tc) in iron-based compounds. Long-term post annealing is the commonly adopted recipe to induce the superconductivity transition in the not-superconductive as-grown FeSe/STO monolayer. Here, we developed a kinetic method, i.e., hydrogen exposure followed by gentle annealing, to enhance the superconductivity of the FeSe/STO monolayer. Our approach is more efficient than the long-term post annealing. Scanning tunneling microscopy (STM) characterization demonstrated the so far largest superconducting gap of similar to 22 mV, indicating an enhanced superconductivity. We believe that the hydrogen-induced lattice Fe diffusion facilitates to remove the interfacial excess Se atoms fatal to the superconductivity, resulting in the formation of a second layer FeSe. The subsequent annealing helps to annihilate the generated Fe vacancies and, thus, enhance the superconductivity in the FeSe/STO monolayer.