We report the superconductivity evolution of one unit cell (1-UC) and 2-UC FeSe films on SrTiO3(001) substrates with potassium (K) adsorption. By in situ scanning tunneling spectroscopy measurement, we find that the superconductivity in 1-UC FeSe films is continuously suppressed with increasing K coverage, whereas non-superconducting 2-UC FeSe films become superconducting with a gap of ~17 meV or ~11 meV depending on whether the underlying 1-UC films are superconducting or not. This work explicitly reveals that the interface electron-phonon coupling is strongly related to the charge transfer at FeSe/STO interface and plays vital role in enhancing Cooper pairing in both 1-UC and 2-UC FeSe films.
@article{arxiv.1509.08950,
title = {Superconductivity dichotomy in K-coated single and double unit cell FeSe films on SrTiO3},
author = {Chenjia Tang and Ding Zhang and Yunyi Zang and Chong Liu and Guanyu Zhou and Zheng Li and Cheng Zheng and Xiaopeng Hu 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:1509.08950},
year = {2015}
}