Role of Equilibrium Fluctuations in Light-Induced Order,Physical Review Letters

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Role of Equilibrium Fluctuations in Light-Induced Order
Physical Review Letters ( IF 8.1 ) Pub Date : 2021-11-24 , DOI: 10.1103/physrevlett.127.227401
Alfred Zong _{1,

2} , Pavel E Dolgirev ₃ , Anshul Kogar _{1,

4} , Yifan Su ₁ , Xiaozhe Shen ₅ , Joshua A W Straquadine _{6,

7,

8} , Xirui Wang ₁ , Duan Luo ₅ , Michael E Kozina ₅ , Alexander H Reid ₅ , Renkai Li ₅ , Jie Yang ₅ , Stephen P Weathersby ₅ , Suji Park _{5,

9} , Edbert J Sie _{7,

8} , Pablo Jarillo-Herrero ₁ , Ian R Fisher _{6,

7,

8} , Xijie Wang ₅ , Eugene Demler _{3,

10} , Nuh Gedik ₁

Affiliation

Engineering novel states of matter with light is at the forefront of materials research. An intensely studied direction is to realize broken-symmetry phases that are “hidden” under equilibrium conditions but can be unleashed by an ultrashort laser pulse. Despite a plethora of experimental discoveries, the nature of these orders and how they transiently appear remain unclear. To this end, we investigate a nonequilibrium charge density wave (CDW) in rare-earth tritellurides, which is suppressed in equilibrium but emerges after photoexcitation. Using a pump-pump-probe protocol implemented in ultrafast electron diffraction, we demonstrate that the light-induced CDW consists solely of order parameter fluctuations, which bear striking similarities to critical fluctuations in equilibrium despite differences in the length scale. By calculating the dynamics of CDW fluctuations in a nonperturbative model, we further show that the strength of the light-induced order is governed by the amplitude of equilibrium fluctuations. These findings highlight photoinduced fluctuations as an important ingredient for the emergence of transient orders out of equilibrium. Our results further suggest that materials with strong fluctuations in equilibrium are promising platforms to host hidden orders after laser excitation.

中文翻译：

平衡波动在光诱导秩序中的作用

用光设计新的物质状态是材料研究的前沿。一个深入研究的方向是实现在平衡条件下“隐藏”但可以通过超短激光脉冲释放的对称破缺相。尽管有大量的实验发现，但这些命令的性质以及它们是如何短暂出现的仍不清楚。为此，我们研究了稀土碲化物中的非平衡电荷密度波 (CDW)，它在平衡状态下被抑制但在光激发后出现。使用在超快电子衍射中实现的泵-泵-探针协议，我们证明光诱导的 CDW 仅由阶参数波动组成，尽管长度尺度不同，但与平衡中的临界波动具有惊人的相似性。通过计算非微扰模型中 CDW 波动的动力学，我们进一步表明光诱导阶的强度受平衡波动幅度的控制。这些发现强调了光致波动是出现不平衡的瞬态顺序的重要因素。我们的结果进一步表明，平衡中具有强烈波动的材料是在激光激发后承载隐藏订单的有希望的平台。

更新日期：2021-11-25

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