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coherent X-ray diffraction imagingresonant X-ray diffraction midinfrared laseroxide heterostructure antiferromagnetism
Abstract:
Imaging the atomic-scale dynamics of thin films is important to develop the next generation of computer technology. Coherent diffraction imaging can provide this information for other dimensionalities, but is unreliable when applied to thin-film measurements. This paper describes an approach to solving this problem using many measurements on a system that is changing in time. As an example, a demagnetization front is imaged as it sweeps through an antiferromagnetic film at twice the speed of sound, leaving a paramagnetic state in its wake. This fast switching is initiated by a midinfrared pulse tuned to the substrate. The recovered magnetization evolution then shows the potential for control of optoelectronic switching devices by driving interface lattice dynamics.Diffraction imaging of nonequilibrium dynamics at atomic resolution is becoming possible with X-ray free-electron lasers. However, there are unresolved problems with applying this method to objects that are confined in only one dimension. Here I show that reliable one-dimensional coherent diffraction imaging is possible by splicing together images recovered from different time delays in an optical pump X-ray probe experiment. The time and space evolution of antiferromagnetic order in a vibrationally excited complex oxide heterostructure is recovered from time-resolved measurements of a resonant soft X-ray diffraction peak. Midinfrared excitation of the substrate is shown to lead to a demagnetization front that propagates at a velocity exceeding the speed of sound, a critical observation for the understanding of driven phase transitions in complex condensed matter.
