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SUMMARY:X-ray free-electron lasers – a new probe for quantum matter
DTSTART;VALUE=DATE:20180713
DTSTAMP:20260510T020944Z
UID:14c195250dfa8683aa4360f9f7baf5aa52365486a9f2bf3dc584b889
CATEGORIES:Conferences - Seminars
DESCRIPTION:Simon Gerber \nThe advent of x-ray free-electron lasers (FEL)
  provides us with a tool to investigate the lattice and electronic dynami
 cs of solids at the inherent time (femtoseconds) and length (Ångströms
 ) scale. This new generation of accelerator-based photon sources delivers
  extremely brilliant\, ultrashort and coherent x-ray pulses that are pri
 marily used to map out ultrafast dynamics\, but also for taking snapshots
  with single x-ray pulses and/or employing their coherence. First\, I wi
 ll introduce the unique properties of x-ray FELs and sketch the current s
 tate-of-the-art in the field of condensed matter\, as well as the progre
 ss of the SwissFEL project. Then\, I will illustrate the capabilities of 
 x-ray FELs at the example of a study from the Linac Coherent Light Source
  (LCLS). \nIdentifying the mechanism that leads to the emergence of sup
 erconductivity in iron-based materials remains the subject of active rese
 arch. Amongst spin-driven scenarios\, it has also been suggested that e
 lectron correlations enhance the electron-phonon coupling in these materi
 als\, but direct experimental verification has been lacking. We show tha
 t the electron-phonon coupling strength in FeSe can be directly quantifie
 d by combining two ultrafast experiments into a “coherent lock-in” m
 easurement in the terahertz regime: x-ray diffraction tracks the light-i
 nduced coherent lattice motion\, while photoemission monitors the cohere
 nt\, orbital-resolved changes in the electronic band structure. Comparis
 on with theory reveals an enhancement of the coupling strength owing to 
 correlation effects\, highlighting the importance of a cooperative interp
 lay between electron-electron and electron-phonon interactions. By relyi
 ng only on a linear\, coherent response\, this approach denotes a purely 
 experimental and model-free technique\, which opens the way for unbiased
  tests of emergent phenomena in correlated materials.\n \nAbout the resea
 rch of the speaker: https://www.psi.ch/lmn/simon-gerber\n 
LOCATION:CE 1 5 https://plan.epfl.ch/?room==CE%201%205
STATUS:CONFIRMED
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