Controlling superconductivity at the FeSe/SrTiO3 interface by interfacial electron density

Single layer iron selenide (FeSe) on SrTiO3 substrate with a possible superconducting transition temperature (T$_{c})$ above 100K has attracted a great deal of attention recently. An important outstanding puzzle in this system is the inconsistency in T$_{c}$ as measured by different techniques. Here we systematically study the dependence of T$_{c}$ on the electron carrier density in this system and found that T$_{c}$ can be most effectively enhanced by increasing the density of electron carriers directly at the FeSe/SrTiO3 interface. We believe that our result resolves some of the puzzles in previous experiments, and open the possibility for further enhancement of T$_{c}$ in this system even when taken outside the UHV chamber.