Alkali-metal (potassium) adsorption on FeSe thin films with thickness from two unit cells (UC) to 4-UC on SrTiO3 grown by molecular beam epitaxy is investigated with a low-temperature scanning tunneling microscope. At appropriate potassium coverage (0.2-0.3 monolayer), the tunneling spectra of the films all exhibit a superconducting-like gap larger than 11 meV (five times the gap value of bulk FeSe), and two distinct features of characteristic phonon modes at 11 meV and 21 meV. The results reveal the critical role of the interface enhanced electron-phonon coupling for possible high temperature superconductivity in the system and is consistent with recent theories. Our study provides compelling evidence for the conventional pairing mechanism for this type of heterostructure superconducting systems.
@article{arxiv.1508.06368,
title = {Interface enhanced electron-phonon coupling and high temperature superconductivity in potassium-coated ultra-thin FeSe films on SrTiO3},
author = {Chenjia Tang and Chong Liu and Guanyu Zhou and Fangsen Li and Ding Zhang and Zheng Li and Canli Song and Shuaihua Ji and Ke He and Xi Chen and Lili Wang and Xucun Ma and Qi-Kun Xue},
journal= {arXiv preprint arXiv:1508.06368},
year = {2016}
}