X-ray resonant scattering studies of orbital and charge ordering in Pr 1 − x Ca x MnO 3
X-ray resonant scattering studies of orbital and charge ordering in Pr 1 − x Ca x MnO 3
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Pr 1 − x Ca x MnO 3 中轨道和电荷排序的 X 射线共振散射研究
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
Y. Tokura
中科院分区：
文献类型：
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作者：
M. Zimmermann;C. Nelson;J. Hill;D. Gibbs;M. Blume;D. Casa;B. Keimer;Y. Murakami;C. Kao;C. Venkataraman;T. Gog;Y. Tomioka;Y. Tokura
我们给出了系统的X射线散射研究结果，研究了${mathrm{Pr}}_{1ensuremath{-}x}{mathrm{Ca}}_{x}{mathrm{MnO}}_{3}$系列锰氧化物的电荷有序性和轨道有序性。在每个样品的有序相中，表征了电荷波矢和轨道波矢上的散射以及晶格常数与温度的关系。与x=0.5样品的电子和中子衍射研究结果形成鲜明对比的是，x=0.4和0.5样品的高动量转移分辨研究进一步表明，虽然存在长程电荷有序性，但长程轨道有序性从未建立。在电荷和轨道有序化温度{T}{0}以上，电荷-有序涨落比轨道涨落具有更高的相关性。这表明在这些样品中，电荷顺序决定了轨道顺序。此外，在x=0.4和0.5的样品中，发现了具有与电荷和轨道有序性相同周期的晶格纵向调制。对于$x=0.25时，只观察到长程轨道有序化，没有电荷有序化的迹象，也没有额外的晶格调制。我们还报道了在磁场作用下对x=0.4的样品的电荷损失和轨道有序性的初步研究结果。最后，在共振极限和非共振极限下表征了这些化合物中电荷和轨道有序度的极化和方位向关系，并与现有理论的预测进行了比较。所得结果与电子结构的团簇密度近似和局域密度近似计算定性一致。
We present the results of a systematic x-ray scattering study of the charge and orbital ordering in the manganite series ${mathrm{Pr}}_{1ensuremath{-}x}{mathrm{Ca}}_{x}{mathrm{MnO}}_{3}$ with $x=0.25,$ 0.4, and 0.5. The temperature dependence of the scattering at the charge and orbital wavevectors, and of the lattice constants, was characterized throughout the ordered phase of each sample. It was found that the charge- and orbital-order wavevectors are commensurate with the lattice, in striking contrast to the results of electron and neutron diffraction studies of samples with $x=0.5.$ High-momentum-transfer resolution studies of the $x=0.4$ and 0.5 samples further revealed that while long-range charge order is present, long-range orbital order is never established. Above the charge and orbital ordering temperature ${T}_{0},$ the charge-order fluctuations are more highly correlated than the orbital fluctuations. This suggests that charge order drives orbital order in these samples. In addition, a longitudinal modulation of the lattice with the same periodicity as the charge and orbital ordering was discovered in the $x=0.4$ and 0.5 samples. For $x=0.25,$ only long-range orbital order was observed with no indication of charge ordering, nor of an additional lattice modulation. We also report the results of a preliminary investigation of the loss of charge and orbital ordering in the $x=0.4$ sample by application of a magnetic field. Finally, the polarization and azimuthal dependence of the charge and orbital ordering in these compounds are characterized both in the resonant and nonresonant limits, and compared with the predictions of current theories. The results are qualitatively consistent with both cluster and local density approximation $+U$ calculations of the electronic structure.