Superconductivity enhancement of FeSe films on substrates with and without Ti-O bonds

Remarkable enhancement of the superconducting transition temperature (T_c) has been observed for monolayer (ML) FeSe films grown on SrTiO₃ substrates, triggering a surge of research excitement. The mechanism for the Tc enhancement has been the central question, as it may present a new strategy for searching for higher T_c materials. In this talk, I will first show the combined studies of interfacial engineering, ARPES studies and synchrotron-based surface X-ray diffraction studies on FeSe/ SrTiO₃ interfaces, through which we reveal the electronic structure ingredients and the atomic-scale structure of ML FeSe/ SrTiO₃. Our results point to the fascinating prospect that cooperation between different Cooper pairing channels may be a general framework to understand and design high-temperature superconductors. Next, I will show the superconductivity and electronic structure studies on more interfaces consisting of FeSe and transition metal oxides without Ti-O bonds. These results not only enrich the family of superconducting interfaces, but also provides a testbed for understanding the key ingredients of interfacial high-temperature superconductivity.