Scanning tunneling spectroscopy has been used to reveal signatures of a bosonic mode in the local quasiparticle density of states of superconducting FeSe films. The mode appears below Tc as a 'dip-hump' feature at energy \Omega ~ 4.7 kBTc beyond the superconducting gap \Delta. Spectra on strained regions of the FeSe films reveal simultaneous decreases in \Delta and \Omega. This contrasts with all previous reports on other high-Tc superconductors, where \Delta locally anti-correlates with \Omega. A local strong coupling model is found to reconcile the discrepancy well, and to provide a unified picture of the electron-boson coupling in unconventional superconductors.
@article{arxiv.1308.2155,
title = {Imaging the Electron-Boson Coupling in Superconducting FeSe},
author = {Can-Li Song and Yi-Lin Wang and Ye-Ping Jiang and Zhi Li and Lili Wang and Ke He and Xi Chen and Jennifer E Hoffman and Xu-Cun Ma and Qi-Kun Xue},
journal= {arXiv preprint arXiv:1308.2155},
year = {2014}
}