Ultrafast observation of critical nematic fluctuations and giant magnetoelastic coupling in iron pnictides
Ultrafast observation of critical nematic fluctuations and giant magnetoelastic coupling in iron pnictides
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DOI：
10.1038/ncomms4229
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发表时间：
2014-02-01
影响因子：
16.6
通讯作者：
Wang, Jigang
中科院分区：
文献类型：
--
作者：
Patz, Aaron;Li, Tianqi;Wang, Jigang
许多铁磷属元素具有强烈的各向异性正常态特性，这对这些材料表现出的奇异磁性和超导行为很重要。然而，所观察到的各向异性的起源尚不清楚。电子驱动的向列性已经被提出，但将其作为独立的自由度与磁性和结构有序区分开来是困难的，因为它们耦合在一起打破了相同的四重对称性。在这里，我们使用时间分辨旋光法来揭示非应变Ba（Fe-1-Co-x（x））（2）As-2的临界涨落。飞秒各向异性响应，这是由两个折叠的平面内各向异性的复折射率，显示了一个特征的两步恢复中没有的各向同性响应。快速恢复只出现在磁有序状态，而缓慢的持续在顺磁相的临界发散接近结构转变温度。动力学还揭示了一个巨大的磁弹性耦合，远远超过电子自旋和电子声子耦合，与传统的磁性金属相反。
Many of the iron pnictides have strongly anisotropic normal-state characteristics, important for the exotic magnetic and superconducting behaviour these materials exhibit. Yet, the origin of the observed anisotropy is unclear. Electronically driven nematicity has been suggested, but distinguishing this as an independent degree of freedom from magnetic and structural orders is difficult, as these couple together to break the same tetragonal symmetry. Here we use time-resolved polarimetry to reveal critical nematic fluctuations in unstrained Ba(Fe-1-Co-x(x))(2)As-2. The femtosecond anisotropic response, which arises from the two-fold in-plane anisotropy of the complex refractive index, displays a characteristic two-step recovery absent in the isotropic response. The fast recovery appears only in the magnetically ordered state, whereas the slow one persists in the paramagnetic phase with a critical divergence approaching the structural transition temperature. The dynamics also reveal a gigantic magnetoelastic coupling that far exceeds electron-spin and electron-phonon couplings, opposite to conventional magnetic metals.