Quasiparticle dynamics and phonon softening in FeSe superconductors

Authors :: Luo, C. W.
Wu, I. H.
Cheng, P. C.
Lin, J-Y
Wu, K. H.
Uen, T. M.
Juang, J. Y.
Kobayashi, T.
Chareev, D. A.
Volkova, O. S.
Vasiliev, A. N.
Source :: Physical Review Letters Vol. 108, 257006 (2012)
Publication Year :: 2012
Abstract: Quasiparticle dynamics of FeSe single crystals revealed by dual-color transient reflectivity measurements ({\Delta}R/R) provides unprecedented information on Fe-based superconductors. The amplitude of fast component in {\Delta}R/R clearly tells a competing scenario between spin fluctuations and superconductivity. Together with the transport measurements, the relaxation time analysis further exhibits anomalous changes at 90 K and 230 K. The former manifests a structure phase transition as well as the associated phonon softening. The latter suggests a previously overlooked phase transition or crossover in FeSe. The electron-phonon coupling constant {\lambda} is found to be 0.16, identical to the value of theoretical calculations. Such a small {\lambda} demonstrates an unconventional origin of superconductivity in FeSe.<br />Comment: Final published version; 5 pages; 4 figures