Insulator to Superconductor Transitions and Strong Electronic Correlations in Single-Layer FeSe/SrTiO$_3$ Films

There has been a debate on whether an appropriate starting point in describing these compounds should go from an itinerant picture or a localized picture. The single-layer FeSe/SrTiO$_3$ films have recently generated great interest for its simplicity of crystal structure and electronic structure, as well as possible high superconducting transition temperature. In this talk, by performing detailed doping-dependent measurements with ARPES, we report an insulator-metal-superconductor transition in the S phase of the single-layer FeSe/SrTiO$_3$ films. The results indicate that strong electronic correlations should be considered in the single-layer FeSe/SrTiO$_3$ films that might be on the verge of Mott physics.