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

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

doi:10.1126/science.aak9946

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

Science. 2017 Jul 7;357(6346):71-75. doi: 10.1126/science.aak9946.

Authors

S Gerber^{1

2}, S-L Yang^{1

3}, D Zhu⁴, H Soifer¹, J A Sobota^{1

5}, S Rebec^{1

3}, J J Lee^{1

3}, T Jia^{1

3}, B Moritz¹, C Jia¹, A Gauthier^{1

3}, Y Li¹, D Leuenberger¹, Y Zhang⁶, L Chaix¹, W Li¹, H Jang⁷, J-S Lee⁷, M Yi⁸, G L Dakovski⁴, S Song⁴, J M Glownia⁴, S Nelson⁴, K W Kim⁹, Y-D Chuang⁵, Z Hussain⁵, R G Moore¹, T P Devereaux¹, W-S Lee¹⁰, P S Kirchmann¹⁰, Z-X Shen^{10

3}

Affiliations

¹ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, CA 94025, USA.
² SwissFEL and Laboratory for Micro and Nanotechnology, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
³ Geballe Laboratory for Advanced Materials, Departments of Physics and Applied Physics, Stanford University, Stanford, CA 94305, USA.
⁴ Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
⁵ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
⁶ International Center for Quantum Materials, Peking University, Beijing 100871, China.
⁷ Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
⁸ Department of Physics, University of California-Berkeley, Berkeley, CA 94720, USA.
⁹ Department of Physics, Chungbuk National University, Cheongju 28644, Korea.
¹⁰ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory and Stanford University, Menlo Park, CA 94025, USA. leews@stanford.edu kirchman@stanford.edu zxshen@stanford.edu.

PMID: 28684521
DOI: 10.1126/science.aak9946

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.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.