超快光致相变中的动力学慢化
Dynamical slowing down in an ultrafast photo-induced phase transition
摘要：
复杂系统由大量相互作用的组分组成，在相变附近通常表现出普遍的行为。某些动态可观测量的减速是在大量背景中发现的一个这样的反复出现的特征。这种现象被称为临界慢化，主要在热力学相变中得到很好的研究。然而，在高度非平衡的情况下，人们对它的了解较少，在这种情况下，穿越相边界所需的时间与动力学涨落的时间尺度相当。利用瞬态光谱和飞秒电子衍射研究了电荷密度波模型化合物LaTe $_3$的光致跃迁。我们观察到，它需要最长的时间来抑制的序参量在阈值光激发密度，CDW瞬时消失。这一发现可以通过将含时朗道理论推广到远离平衡的系统来定量地捕捉。对动力学慢化的实验观察和理论理解可能会提供对多体系统中非平衡相变背后的其他一般原理的深入了解。
英文摘要：
Complex systems, which consist of a large number of interacting constituents, often exhibit universal behavior near a phase transition. A slowdown of certain dynamical observables is one such recurring feature found in a vast array of contexts. This phenomenon, known as critical slowing down, is well studied mostly in thermodynamic phase transitions. However, it is less understood in highly nonequilibrium settings, where the time it takes to traverse the phase boundary becomes comparable to the timescale of dynamical fluctuations. Using transient optical spectroscopy and femtosecond electron diffraction, we studied a photo-induced transition of a model charge-density-wave (CDW) compound, LaTe$_3$. We observed that it takes the longest time to suppress the order parameter at the threshold photoexcitation density, where the CDW transiently vanishes. This finding can be quantitatively captured by generalizing the time-dependent Landau theory to a system far from equilibrium. The experimental observation and theoretical understanding of dynamical slowing down may offer insight into other general principles behind nonequilibrium phase transitions in many-body systems.
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