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首页> 外文期刊>Physical Review X >Structural Evidence for Ultrafast Polarization Rotation in Ferroelectric/Dielectric Superlattice Nanodomains
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Structural Evidence for Ultrafast Polarization Rotation in Ferroelectric/Dielectric Superlattice Nanodomains

机译：铁电/介电超晶纳米型超快偏振旋转的结构证据

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Weakly coupled ferroelectric/dielectric superlattice thin-film heterostructures exhibit complex nanoscale polarization configurations that arise from a balance of competing electrostatic, elastic, and domain-wall contributions to the free energy. A key feature of these configurations is that the polarization can locally have a significant component that is along the thin-film surface normal direction with an overall configuration maintaining zero net in-plane polarization. PbTiO 3 / SrTiO 3 thin-film superlattice heterostructures on a conducting SrRuO 3 bottom electrode on SrTiO 3 have a room-temperature stripe nanodomain pattern with a nanometer-scale lateral period. Ultrafast time-resolved x-ray free electron laser diffraction and scattering experiments reveal that above-bandgap optical pulses induce propagating acoustic pulses and a perturbation of the domain diffuse scattering intensity arising from the nanoscale stripe domain configuration. With 400-nm optical excitation, two separate acoustic pulses are observed: a high-amplitude pulse resulting from strong optical absorption in the bottom electrode and a weaker pulse arising from the depolarization-field-screening effect due to absorption directly within the superlattice. The picosecond scale variation of the nanodomain diffuse scattering intensity is consistent with a larger polarization change than would be expected due to the polarization-tetragonality coupling of uniformly polarized ferroelectrics. The polarization change is consistent, instead, with polarization rotation facilitated by the reorientation of the in-plane component of the polarization at the domain boundaries of the striped polarization structure. The complex steady-state configuration within these ferroelectric heterostructures leads to ultrafast polarization rotation phenomena that have previously been available only through the selection of bulk crystal composition.
机译：弱耦合铁电/介电超晶格薄膜异质结构表现出从竞争静电，弹性和畴壁贡献的平衡而产生的复合纳米级极化配置。这些配置的一个关键特征是，偏振可以局部地具有沿着薄膜表面法线方向的重要组件，其具有保持零网面内极化的整体配置。 PBTIO 3 / SRTIO 3在SRTIO 3上导电Srruo 3底部电极上的薄膜超晶格异质结构具有室温条纹纳米域图案，具有纳米级横向周期。超快时间分辨X射线自由激光衍射和散射实验表明，带隙光学脉冲诱导传播声学脉冲和从纳米级条纹域构造产生的域漫射散射强度的扰动。利用400nm光学激发，观察到两个单独的声脉冲：由于直接在超晶格内的吸收而​​导致的底部电极中强的光学吸收和较弱的脉冲产生的高幅度脉冲。纳米域漫射散射强度的皮秒缩放变化与均匀极化铁路的偏振 - 四边形耦合导致的偏振变化比预期的偏振变化一致。偏振变化是一致的，而是通过在条纹偏振结构的畴边界处的平面内分量的重新定向而促进的偏振旋转。这些铁电异质结构内的复杂稳态配置导致超快偏振旋转现象，其仅通过选择散装晶体组合物而获得。

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