Monolayer FeSe films grown on SrTiO3 with controlled surface superstructures studied by scanning probes: evidence for interface superconductivity

Abstract

Abstract Superconductivity in atomically thin films has attracted great attention, but the superconducting transition temperature T c is generally lower than that of the bulk. In this respect, the FeSe films grown on SrTiO3 (STO) substrate have attracted much attention because the T c was reported as high as 40–109 K when the thickness was decreased to a monolayer (single unit cell, 1 UC). Since the T c of the bulk is only 8 K, this value is much higher and the mechanism of this high-temperature superconductivity has been under intensive study, but has yet to be clarified. In this review, we present our detailed study on this 1 UC FeSe/STO system using two different types of scanning probes. By taking great care of the control of the STO surface, we show that the superconductivity is localized at the interface of FeSe and STO.