High-T_c superconductivity in monolayer FeSe on SrTiO₃ via interface-induced small-q electron-phonon coupling

A monolayer of FeSe deposited on SrTiO₃ becomes superconducting at temperatures that exceed T_c=100 K, as compared to a bulk T_c of 8 K. Recent ARPES measurements have provided strong evidence that an interfaced-induced electron-phonon interaction between FeSe electrons and SrTiO₃ phonons plays a decisive role in this phenomenon. However, the mechanism that drives this tantalizing high-T_c boost is still unclear. Here, we examine the recent experimental findings using fully anisotropic, full bandwidth multiband Eliashberg calculations focusing on the superconducting state of FeSe/STO. We use a realistic ten band tight-binding band structure for the electrons of monolayer FeSe and study how the suggested interface-induced small-q electron-phonon interaction mediates superconductivity. Our calculations produce a high-T_c s-wave superconducting state with the experimentally resolved momentum dependence. Further, we calculate the normal metal/insulator/superconductor tunneling spectrum and identify fingerprints of the interface-induced phonon mechanism.