The functional properties of complex oxides, including magnetism and ferroelectricity, are closely linked to subtle structural distortions. Ultrafast optical excitations provide the means to manipulate structural features and ultimately to affect the functional properties of complex oxides with picosecond-scale precision. We report that the lattice expansion of multiferroic BiFeO₃ following above-bandgap optical excitation leads to distortion of the oxygen octahedral rotation (OOR) pattern. The continuous coupling between OOR and strain was probed using time-resolved X-ray free-electron laser diffraction with femtosecond time resolution. Density functional theory calculations predict a relationship between the OOR and the elastic strain consistent with the experiment, demonstrating a route to employing this approach in a wider range of systems. Ultrafast control of the functional properties of BiFeO₃ thin films is enabled by this approach because the OOR phenomena are related to ferroelectricity, and via the Fe–O–Fe bond angles, the superexchange interaction between Fe atoms.

中文翻译：

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多铁性 BiFeO3 薄膜中氧八面体旋转的超快光致扰动


复杂氧化物的功能特性，包括磁性和铁电性，与微妙的结构扭曲密切相关。超快光激发提供了操纵结构特征并最终以皮秒级精度影响复杂氧化物功能特性的方法。我们报告了多铁性 BiFeO ₃ 在带隙以上光激发后的晶格膨胀导致氧八面体旋转 (OOR) 图案的扭曲。使用具有飞秒时间分辨率的时间分辨 X 射线自由电子激光衍射来探测 OOR 和应变之间的连续耦合。密度泛函理论计算预测了 OOR 与弹性应变之间的关系，与实验一致，展示了在更广泛的系统中采用这种方法的途径。这种方法可以实现对 BiFeO ₃ 薄膜功能特性的超快控制，因为 OOR 现象与铁电性有关，并且通过 Fe-O-Fe 键角与 Fe 原子之间的超交换相互作用有关。