Mangu Anudeep, Stoica Vladimir A, Zheng Hao, Yang Tiannan, Zhang Maohua, Wang Huaiyu Hugo, Zu Rui, Nguyen Quynh L, Song Sanghoon, Das Sujit, Meisenheimer Peter, Donoway Elizabeth, Chollet Matthieu, Sun Yanwen, Turner Joshua J, Freeland John W, Wen Haidan, Martin Lane W, Chen Long-Qing, Gopalan Venkatraman, Zhu Diling, Cao Yue, Lindenberg Aaron M
Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305.
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA 94025.
Proc Natl Acad Sci U S A. 2025 Jan 14;122(2):e2407772122. doi: 10.1073/pnas.2407772122. Epub 2025 Jan 8.
A central paradigm of nonequilibrium physics concerns the dynamics of heterogeneity and disorder, impacting processes ranging from the behavior of glasses to the emergent functionality of active matter. Understanding these complex mesoscopic systems requires probing the microscopic trajectories associated with irreversible processes, the role of fluctuations and entropy growth, and the timescales on which nonequilibrium responses are ultimately maintained. Approaches that illuminate these processes in model systems may enable a more general understanding of other heterogeneous nonequilibrium phenomena, and potentially define ultimate speed and energy cost limits for information processing technologies. Here, we apply ultrafast single-shot X-ray photon correlation spectroscopy to resolve the nonequilibrium, heterogeneous, and irreversible mesoscale dynamics during a light-induced phase transition in a (PbTiO)/(SrTiO) superlattice. Such ferroelectric superlattice systems are a useful platform to study phase transitions and topological dynamics due to their high degree of tunability. This provides an approach for capturing the nucleation of the light-induced phase, the formation of transient mesoscale defects at the boundaries of the nuclei, and the eventual annihilation of these defects, even in systems with complex polarization topologies. We identify a nonequilibrium correlation response spanning >10 orders of magnitude in timescales, with multistep behavior similar to the plateaus observed in supercooled liquids and glasses. We further show how the observed time-dependent long-time correlations can be understood in terms of stochastic and non-Markovian dynamics of domain walls, encoded in waiting-time distributions with power-law tails. This work defines possibilities for probing the nonequilibrium and correlated dynamics of disordered and heterogeneous media.
非平衡态物理学的一个核心范式涉及非均匀性和无序性的动力学，其影响范围涵盖从玻璃的行为到活性物质的涌现功能等各种过程。理解这些复杂的介观系统需要探究与不可逆过程相关的微观轨迹、涨落和熵增长的作用，以及非平衡响应最终得以维持的时间尺度。在模型系统中阐明这些过程的方法，可能有助于更全面地理解其他非均匀非平衡现象，并有可能为信息处理技术定义最终的速度和能量成本极限。在此，我们应用超快单次X射线光子相关光谱技术，来解析(PbTiO)/(SrTiO)超晶格中光致相变过程中的非平衡、非均匀和不可逆介观动力学。由于其高度的可调谐性，这种铁电超晶格系统是研究相变和拓扑动力学的有用平台。这提供了一种方法，即使在具有复杂极化拓扑结构的系统中，也能捕捉光致相的成核、核边界处瞬态介观缺陷的形成以及这些缺陷的最终湮灭。我们识别出一种跨越超过10个数量级时间尺度的非平衡相关响应，其多步行为类似于在过冷液体和玻璃中观察到的平台期。我们进一步表明，如何根据畴壁的随机和非马尔可夫动力学来理解所观察到的随时间变化的长时间相关性，这种动力学编码在具有幂律尾部的等待时间分布中。这项工作为探究无序和非均匀介质的非平衡和相关动力学定义了可能性。
