皮秒体积膨胀驱动纳米织构莫特绝缘体中的延迟绝缘体-金属转变
Picosecond volume expansion drives a later-time insulator-metal transition in a nano-textured Mott Insulator
AI总结：
本研究通过时间分辨X射线衍射与反射率测量，揭示了外延应变Ca2RuO4薄膜中光致绝缘体-金属转变的延迟机制，指出皮秒体积膨胀及晶格动力学在无畴形成条件下主导转变过程，并强调了应变对时间尺度的调控作用。
摘要：
技术正朝着在物质的不同电子和磁态之间进行更快切换的方向发展。以太赫兹速率操控性质需要访问电子的固有时间尺度（飞秒）及相关声子的时间尺度（几十飞秒到几皮秒），这可以通过短脉冲光激发实现。然而，在许多莫特绝缘体中，电子转变伴随着晶格结构改变的分形畴的成核与生长，导致经验时间尺度由缓慢的粗化动力学主导。在此，我们利用时间分辨X射线衍射和反射率测量，研究外延应变薄膜莫特绝缘体Ca2RuO4中的光致绝缘体-金属转变。该动力学转变在没有可观察的畴形成和粗化效应的情况下发生，从而允许研究固有的电子和晶格动力学。在通量阈值之上，初始电子激发驱动快速的晶格重排，随后是较慢的电子演化进入亚稳态非平衡态。基于时间依赖动力学平均场理论和半经典晶格动力学，在最近发表的平衡能量景观图景内进行的微观计算解释了阈值行为，并阐明了电子相变延迟起始与复合的运动学约束。卫星散射峰的分析表明，光激发薄膜中保留了应变诱导的纳米织构。这项工作强调了结合电子和结构研究以揭示动态转变物理的重要性，并阐明了应变在调节光诱导过程时间尺度中的作用。
英文摘要：
Technology moves towards ever faster switching between different electronic and magnetic states of matter. Manipulating properties at terahertz rates requires accessing the intrinsic timescales of electrons (femtoseconds) and associated phonons (10s of femtoseconds to few picoseconds), which is possible with short-pulse photoexcitation. Yet, in many Mott insulators, the electronic transition is accompanied by the nucleation and growth of percolating domains of the changed lattice structure, leading to empirical time scales dominated by slow coarsening dynamics. Here, we use time-resolved X-ray diffraction and reflectivity measurements to investigate the photoinduced insulator-to-metal transition in an epitaxially strained thin film Mott insulator Ca2RuO4. The dynamical transition occurs without observable domain formation and coarsening effects, allowing the study of the intrinsic electronic and lattice dynamics. Above a fluence threshold, the initial electronic excitation drives a fast lattice rearrangement, followed by a slower electronic evolution into a metastable non-equilibrium state. Microscopic calculations based on time-dependent dynamical mean-field theory and semiclassical lattice dynamics within a recently published equilibrium energy landscape picture explain the threshold-behavior and elucidate the delayed onset of the electronic phase transition in terms of kinematic constraints on recombination. Analysis of satellite scattering peaks indicates the persistence of a strain-induced nano-texture in the photoexcited film. This work highlights the importance of combined electronic and structural studies to unravel the physics of dynamic transitions and elucidates the role of strain in tuning the timescales of photoinduced processes.
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