Material functionality can be strongly determined by structure extending only over nanoscale distances. The pair distribution function presents an opportunity for structural studies beyond idealized crystal models and to investigate structure over varying length scales. Applying this method with ultrafast time resolution has the potential to similarly disrupt the study of structural dynamics and phase transitions. Here we demonstrate such a measurement of CuIr₂S₄ optically pumped from its low-temperature Ir-dimerized phase. Dimers are optically suppressed without spatial correlation, generating a structure whose level of disorder strongly depends on the length scale. The redevelopment of structural ordering over tens of picoseconds is directly tracked over both space and time as a transient state is approached. This measurement demonstrates the crucial role of local structure and disorder in non-equilibrium processes as well as the feasibility of accessing this information with state-of-the-art XFEL facilities.

材料的功能可以通过仅在纳米级距离上延伸的结构来强烈确定。对分布函数为超越理想晶体模型的结构研究和研究不同长度尺度的结构提供了机会。应用这种具有超快时间分辨率的方法有可能类似地扰乱结构动力学和相变的研究。在这里，我们演示了从低温 Ir 二聚相中光泵浦的 CuIr ₂ S ₄ 的测量。二聚体在没有空间相关性的情况下被光学抑制，产生一种结构，其无序程度强烈依赖于长度尺度。当接近瞬态时，在空间和时间上直接跟踪数十皮秒内结构排序的重建。该测量证明了局部结构和无序在非平衡过程中的关键作用，以及利用最先进的 XFEL 设施获取这些信息的可行性。