Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan.
Phys Rev Lett. 2012 Jun 22;108(25):257006. doi: 10.1103/PhysRevLett.108.257006. Epub 2012 Jun 20.
Quasiparticle dynamics of FeSe single crystals revealed by dual-color transient reflectivity measurements (ΔR/R) provides unprecedented information on Fe-based superconductors. The amplitude of the fast component in ΔR/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.
双色瞬态反射率测量（ΔR/R）揭示的 FeSe 单晶准粒子动力学为铁基超导体提供了前所未有的信息。ΔR/R 中快分量的振幅清楚地给出了自旋涨落和超导之间的竞争情景。结合输运测量，弛豫时间分析进一步在 90 和 230 K 处表现出异常变化。前者表现为结构相变以及相关的声子软化。后者表明在 FeSe 中存在一个以前被忽视的相变或交叉。电子-声子耦合常数 λ 被发现为 0.16，与理论计算值相同。如此小的 λ 表明了 FeSe 中超导的非常规起源。
