Quasiparticle Dynamics and Phonon Softening in FeSe Superconductors

C. W. Luo (羅志偉), I. H. Wu (吳易修), P. C. Cheng (鄭博仲), J.-Y. Lin (林俊源), K. H. Wu (吳光雄), T. M. Uen (溫增明), J. Y. Juang (莊振益), T. Kobayashi, D. A. Chareev, O. S. Volkova, and A. N. Vasiliev

Phys. Rev. Lett. 108, 257006 – Published 20 June 2012

Abstract

Quasiparticle dynamics of FeSe single crystals revealed by dual-color transient reflectivity measurements ( $Δ R / R$ ) provides unprecedented information on Fe-based superconductors. The amplitude of the fast component in $Δ R / R$ clearly gives a competing scenario between spin fluctuations and superconductivity. Together with the transport measurements, the relaxation time analysis further exhibits anomalous changes at 90 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 $λ$ is found to be 0.16, identical to the value of theoretical calculations. Such a small $λ$ demonstrates an unconventional origin of superconductivity in FeSe.

Received 5 December 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.257006

Authors & Affiliations

C. W. Luo (羅志偉)^1,*, I. H. Wu (吳易修)¹, P. C. Cheng (鄭博仲)¹, J.-Y. Lin (林俊源)², K. H. Wu (吳光雄)¹, T. M. Uen (溫增明)¹, J. Y. Juang (莊振益)¹, T. Kobayashi^1,3, D. A. Chareev⁴, O. S. Volkova⁵, and A. N. Vasiliev⁵

¹Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan
²Institute of Physics, National Chiao Tung University, Hsinchu 300, Taiwan
³Advanced Ultrafast Laser Research Center, and Department of Engineering Science, Faculty of Informatics and Engineering, University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan
⁴Institute of Experimental Mineralogy, Chernogolovka, Moscow Region, 142432, Russia
⁵Low Temperature Physics and Superconductivity Department, Moscow State University, 119991 Moscow, Russia

^*cwluo@mail.nctu.edu.tw

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Vol. 108, Iss. 25 — 22 June 2012

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