High-temperature superconductivity at the FeSe/SrTiO3 interface

In several recent experiments the superconducting gap of a single-unit-cell-thick FeSe film on SrTiO3 substrate has been observed by scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy. The value of the superconducting gap is about nine times larger than that of the bulk FeSe under ambient pressure, suggesting a much higher pairing energy scale and T-c than all other iron-based superconductors and thus calling for a better understanding of its superconducting mechanism. In this paper we study the effects of screening due to the SrTiO3 ferroelectric phonons on Cooper pairing in FeSe. We conclude that it can significantly enhance the energy scale of Cooper pairing and even change the pairing symmetry. Our results also raise some concerns on whether phonons can be completely ignored for bulk iron-based superconductors.