The interaction of light with materials is an intensively studied research forefront, in which the coupling of radiation energy to selective degrees of freedom offers contact-free tuning of functionalities on ultrafast time scales. Capturing the fundamental processes and understanding the mechanism of photoinduced structural rearrangement are essential to applications such as photo-active actuators and efficient photovoltaic devices. Using ultrafast x-ray absorption spectroscopy aided by density functional theory calculations, we reveal the local structural arrangement around the transition metal atom in a unit cell of the photoferroelectric archetype BiFeO3 film. The out-of-plane elongation of the unit cell is accompanied by the in-plane shrinkage with minimal change of interaxial lattice angles upon photoexcitation. This anisotropic elastic deformation of the unit cell is driven by localized electric field as a result of photoinduced charge separation, in contrast to a global lattice constant increase and lattice angle variations as a result of heating. The finding of a photoinduced elastic unit cell deformation elucidates a microscopic picture of photocarrier-mediated non-equilibrium processes in polar materials.

中文翻译：

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捕获BiFeO3的超快光致局部结构变形。

光与材料的相互作用是一项经过深入研究的前沿技术，其中辐射能与选择性自由度的耦合提供了在超快速度时标上进行功能的无接触调整。捕获基本过程并了解光致结构重排的机理对于诸如光敏致动器和高效光伏设备之类的应用至关重要。在密度泛函理论计算的帮助下，使用超快X射线吸收光谱法，我们揭示了光铁电原型BiFeO3膜的晶胞中过渡金属原子周围的局部结构排列。晶胞的平面外伸长伴随着平面内收缩，并且在光激发时轴向间晶格角的变化最小。与光诱导的电荷分离的结果相比，局部电场驱动这种单电池的各向异性弹性变形，这与加热导致的整体晶格常数增加和晶格角变化相反。光诱导弹性晶胞变形的发现阐明了极性材料中光载体介导的非平衡过程的显微照片。