Ambipolar Doping of Monolayer FeSe by Interface Engineering

Abstract

We report on ambipolar modulation doping of monolayer FeSe epitaxial films grown by molecular beam epitaxy and in situ spectroscopic measurements via a cryogenic scanning tunneling microscopy. It is found that hole doping kills superconductivity in monolayer FeSe films on metallic Ir(001) substrates, whereas electron doping from polycrystalline IrO2/SrTiO3 substrate enhances significantly the superconductivity with an energy gap of 10.3 meV. By exploring substrate-dependent superconductivity, we elucidate the essential impact of substrate work functions on the superconductivity of monolayer FeSe films. Our results therefore offer a valuable reference guide for further enhancement of the transition temperature T c in FeSe-based superconductors by interface engineering.