Spatiotemporal Fluctuations in Transition Metal Oxides

技术摘要：该个人研究者奖支持使用相干软x射线散射在介观长度尺度和时间尺度上对过渡金属氧化物的时空波动进行实验研究。 例如，在锰氧化物中，原子尺度的耦合导致涉及1-2 nm尺度上的自旋、电荷和轨道排序的多个相。 在这些相之间的自由能差小的相边界附近，经常观察到介观相分离，导致10 - 1000 nm尺度上的无序相不均匀性。 最后，这些介观结构的动态响应被认为在复杂的宏观性质，如巨磁电阻中起着关键作用。 我们特别感兴趣的是探索无序中尺度系统特有的预期异常动力学，并将我们的结果与现有的传输和热力学测量联系起来。 具体计划的实验包括测量电荷，自旋和轨道有序相的波动，以及测量居里温度附近的耦合极化波动作为合金成分的函数。 非技术摘要：掺杂的过渡金属氧化物化合物提供了一个很好的例子，说明复杂的层次相互作用如何导致有趣和有用的材料特性。 例如，在锰氧化物中，原子尺度的相互作用导致许多相在几纳米尺度上具有不同的磁性和结构顺序。 在相边界附近，这些相之间的能量差很小，经常观察到介观相分离，导致10 - 1000 nm尺度上的无序相不均匀性。 最后，这些介观结构的动态响应被认为在复杂的宏观性质，如巨磁电阻中起着关键作用。 这项由个人研究者提案支持的工作将探索这种层次结构中最不为人所知的部分-复杂性从有序的微观相到无序的介观结构的方式。 相干软X射线束将被应用于完成这种理解，使用动态激光散射的X射线模拟，这是一种经常用于研究较长长度尺度材料的技术。

Technical abstract:This individual investigator award supports experimental investigations of the spatiotemporal fluctuations in transition metal oxides on the mesoscopic length scale and on time scales longer than one microsecond using coherent soft x-ray scattering. In manganites, for example, atomic-scale couplings lead to a multitude of phases involving spin, charge, and orbital ordering on a scale of 1-2 nm. Near phase boundaries, where the free energy difference between these phases is small, mesoscopic phase separation is often observed, leading to disordered phase heterogeneity on a scale of 10 - 1000 nm. Finally, the dynamical response of these mesoscopic structures is thought to play a key role in complex macroscopic properties like colossal magnetoresistance. We are particularly interested in probing the expected anomalous dynamics endemic to disordered mesoscale systems, and in relating our results to existing transport and thermodynamic measurements. Specific planned experiments include measurement of fluctuations in charge-, spin-, and orbital-ordered phases, and measurement of coupled polaronic fluctuations near the Curie temperature as a function of alloy composition. Non-technical abstract:Doped transition metal oxide compounds offer excellent examples of how complex hierarchical interactions can lead to interesting and useful material properties. In manganites, for example, atomic-scale interactions lead to many phases with varying magnetic and structural orderings on the scale of a few nanometers. Near phase boundaries, where the energy difference between these phases is small, mesoscopic phase separation is often observed, leading to disordered phase heterogeneity on a scale of 10 - 1000 nm. Finally, the dynamical response of these mesoscopic structures is thought to play a key role in complex macroscopic properties like colossal magnetoresistance. The work supported by this individual investigator proposal will probe the most poorly understood part of this hierarchy - the way in which complexity emerges from ordered microscopic phases into poorly ordered mesoscopic structures. Coherent soft x-ray beams will be applied to do accomplish this understanding using the x-ray analog of dynamic laser light scattering, a technique often used to study materials at longer length scales.