Magic Doping and Robust Superconductivity in Monolayer FeSe on Titanates.

The enhanced superconductivity in monolayer FeSe on titanates opens a fascinating pathway toward the rational design of high-temperature superconductors. Utilizing the state-of-the-art oxide plus chalcogenide molecular beam epitaxy systems connected to a synchrotron angle-resolved photoemission spectroscope, epitaxial LaTiO layers with varied atomic thicknesses are inserted between monolayer FeSe and SrTiO, for systematic modulation of interfacial chemical potential. With the dramatic increase of electron accumulation at the LaTiO/SrTiO surface, providing a substantial surge of work function mismatch across the FeSe/oxide interface, the charge transfer and the superconducting gap in the monolayer FeSe are found to remain markedly robust. This unexpected finding indicate the existence of an intrinsically anchored "magic" doping within the monolayer FeSe systems.