标题: | 利用时间解析飞秒光谱研究掺碲硒化铁超导体之超快动力学 Study of Ultrafast Dynamics in FeSexTe1-x Superconductors by Using Time-Resolved Femtosecond Spectroscopy |
作者: | 吴易修 Wu, I-Hsiu 罗志伟 Luo, Chi-Wei 电子物理系所 |
关键字: | 铁基超导体;时间解析飞杪光谱;超快雷射;iron-based superconductor;time-resolved femtosecond sepctroscopy;ultrafast laser |
公开日期: | 2010 |
摘要: | 在本篇论文里,我们利用时间解析飞秒光谱来研究不同碲掺杂的硒化铁(FeSexTe1-x)单晶-即所谓的11型铁基超导体的超快动力学。在400 nm的光激发及800 nm的光探测下,我们可以量测FeSe0.760,FeSe0.166Te0.666,和FeTe0.875单晶在不同温之瞬时反射率变化(ΔR/R)。整体来说,11型铁基超导的ΔR/R光谱中包括两个讯号,一个是准粒子的弛缓过程,另一个是声频声子的振荡信号。不过这些特征会随着Te的掺杂而改变,以具有超导特性的FeSe0.76,FeSe0.166Te0.666样品而言,ΔR/R的大小在Tc及100 K附近(结构相变发生处)有不寻常的增加。而且透过曲线拟合,我们可以获得准粒子的弛缓时间同时算出电子声子(A1g mode)的耦合强度λ,在20 K时,FeSe0.760单晶的λ=0.129,而FeSe0.166Te0.666单晶的λ=0.080。此外,ΔR/R中振荡信号所对应的声频能量亦有不寻常的减小,称之为声子软化(phonon softening)现象。然而上述之变化并未在不具超导特性的样品FeTe0.875单晶上观察到。因此,我们推测11型铁基超导体(FeSexTe1-x)在正常态(约100 K)所出现的声子软化现象与形成超导有密切的关系。 In this dissertation, we used time-resolved femtosecond spectroscopy to study the ultrafast dynamics of FeSexTe1-x single crystals, i.e. 11 type iron-based superconductors. The transient reflectivity (ΔR/R) of FeSe0.760, FeSe0.166Te0.666, and FeTe0.875 single crystals has been performed by 400 nm pump-800 nm probe at various temperatures. In general, the typical ΔR/R of 11 type iron-based superconductors includes two significant components. One is the relaxation of photoinduced quasiparticles. The other is the oscillation component due to the acoustic phonon. Interestingly, these characteristics in ΔR/R are strongly changed by the content of Te in FeSe single crystals. For FeSe0.760 and FeSe0.166Te0.666 single crystals, the abnormal changes in the amplitude of ΔR/R are clearly observed at Tc and around 100 K where the structure-phase transition occurred. Also, the electron-phonon(A1g mode) coupling constant can be estimated to be 0.129 and 0.080, respectively, from the relaxation time ΔR/R. Moreover, the acoustic phonon energy estimated from the period of oscillation in ΔR/R markedly shrinks at Tc and around 100 K, which is the so-called phonon softening. However, above phenomena are not observed in the non-superconducting FeTe0.875 single crystals. Therefore, these results imply that the phonon softening occurred in normal state may be intimately correlated to the superconductivity of 11 type iron-based superconductors. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT079821511 http://hdl.handle.net/11536/47440 |
显示于类别: | Thesis |