Interfacial superconductivity and a Se-vacancy ordered insulating phase in FeSe/Pb Ox heterostructures

The discovery of high-temperature superconductivity in FeSe/SrTiO3 has sparked significant interest in exploring superconducting systems with engineered interfaces. Here, using molecular beam epitaxy growth, we successfully fabricate FeSe/PbOx heterostructures and discover superconductivities in three different monolayer FeSe-related interfaces. We observe superconducting gaps of 13-14 meV in the monolayer FeSe films grown on two different phases of PbOx. Moreover, we discover an insulating Fe10Se9 phase with an ordered √5 × √5 Se-vacancy structure. Our first-principles calculation suggests that this insulating phase originates from electronic correlation. Intriguingly, an additional monolayer FeSe film grown on insulating Fe10Se9 also exhibits superconductivity with the gap size of 5 meV. Our results suggest that the work function differences between monolayer FeSe and the substrates, which can induce band bending and charge transfer, are crucial for interfacial superconductivity.