Abstract
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.
| Original language | English |
|---|---|
| Pages (from-to) | 71-75 |
| Number of pages | 5 |
| Journal | Science |
| Volume | 357 |
| Issue number | 6346 |
| DOIs | |
| State | Published - Jul 7 2017 |
| Externally published | Yes |
Funding
Use of the LCLS, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES) under contract DE-AC02-76SF00515. S.G., S.-L.Y., H.S., J.A.S., S.R., J.J.L., T.J., B.M., C.J., A.G., Y.L., D.L., L.C., W.L., R.G.M., T.P.D., W.-S.L., P.S.K., and Z.-X.S. were supported by the DOE-BES Division of Materials Sciences and Engineering under contract DE-AC02-76SF00515 (to the Stanford Institute for Materials and Energy Sciences). The authors gratefully acknowledge technical assistance at LCLS by D. Stefanescu and R. Fiebich. S.G. and D.L. acknowledge partial support by the Swiss National Science Foundation under fellowships P2EZP2_148737 and P300P2_151328, respectively. S.-L.Y. acknowledges support by the Stanford Graduate Fellowship. H.S. acknowledges support from the Fulbright Scholar Program. A.G. acknowledges support by the National Defense Science and Engineering Graduate Fellowship Program. K.W.K. was supported by the Basic Science Research Program through the National Research Foundation of Korea, funded by the Ministry of Science, ICT and Future Planning (NRF-2015R1A2A1A10056200). Y.-D.C. and Z.H. were supported by the Director, Office of Science, BES, of the U.S. DOE under contract DE-AC02-05CH11231. Raw data from the time-resolved x-ray scattering experiment are kept at the LCLS. Time-resolved photoemission raw data are kept at the Shen Laboratory of Stanford University.