Spatiotemporal Fluctuations in Transition Metal Oxides

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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.