Spatiotemporal Fluctuations in Transition Metal Oxides

技术摘要：这一个人研究人员奖支持使用相干软x射线散射在介观长度尺度和长于一微秒的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了大量的相，包括自旋、电荷和轨道在1-2纳米尺度上的有序。在相界附近，这些相之间的自由能差很小，经常观察到介观相分离，导致10-1000 nm尺度的无序相不均匀。最后，这些介观结构的动力学响应被认为在巨磁电阻等复杂的宏观性质中起着关键作用。我们特别感兴趣的是探索无序中尺度系统特有的预期反常动力学，并将我们的结果与现有的输运和热力学测量联系起来。具体的计划实验包括测量电荷有序相、自旋有序相和轨道有序相的波动，以及测量居里温度附近的耦合极化子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很好的例子，说明复杂的层级相互作用如何产生有趣和有用的材料性能。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有序。在相界附近，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尺度的无序相不均匀。最后，这些介观结构的动力学响应被认为在巨磁电阻等复杂的宏观性质中起着关键作用。这项由个人研究人员提案支持的工作将探索这一层次中最鲜为人知的部分--复杂性从有序的微观相出现到无序的介观结构的方式。相干软X射线束将被应用来完成这一理解，使用动态激光光散射的X射线模拟，这是一种经常用于在较长尺度上研究材料的技术。

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.