Journal Article

Femtosecond electron-phonon lock-in by photoemission and x-ray free-electron laser

Lee, W.-S., Jia, C., Li, W., Li, Y., Sobota, J. A., Zhang, Y., Yang, S.-L., Gauthier, A., Jia, T., Glownia, J. M., Lee, J.-S., Yi, M., Kirchmann, P. S., Jang, H., Soifer, H., Kim, K. W., Shen, Z.-X., Moritz, B., Zhu, D., Dakovski, G. L., Song, S., Gerber, S., Moore, R. G., Leuenberger, D., Hussain, Z., Devereaux, T. P., Nelson, S., Lee, J. J., Rebec, S., Chaix, L., Chuang, Y.-D.

2017

Overview

The interactions that lead to the emergence of superconductivity in iron-based materials remain a subject of debate. It has been suggested that electron-electron correlations enhance electron-phonon coupling in iron selenide (FeSe) and related pnictides, but direct experimental verification has been lacking. Here we show that the electron-phonon coupling strength in FeSe can be quantified by combining two time-domain experiments into a “coherent lock-in” measurement in the terahertz regime. X-ray diffraction tracks the light-induced femtosecond coherent lattice motion at a single phonon frequency, and photoemission monitors the subsequent coherent changes in the electronic band structure.Comparison with theory reveals a strong enhancement of the coupling strength in FeSe owing to correlation effects. Given that the electron-phonon coupling affects superconductivity exponentially, this enhancement highlights the importance of the cooperative interplay between electron-electron and electron-phonon interactions.

• Publisher: American Association for the Advancement of Science,The American Association for the Advancement of Science,American Association for the Advancement of Science (AAAS)
• Subject: Condensed Matter / Coupling / Electron phonon interactions / Elementary excitations / Free electron lasers / Group 5A compounds / Iron / Light diffraction / Light effects / Phonons / Photoelectric emission / Physics / Selenide / Spectroscopy / Superconductivity / Superconductors / X-ray diffraction