X-ray probes of coherence and what they can tell us about coupling and phase transitions

I will talk about two recent examples of experiments where both time-resolved x-ray diffraction and spectroscopy are applied to study coherent dynamics in materials, highlighting the ways in which specific aspects of that coherence manifest in the different techniques. In CoF2, a material with antiferromagnetic order that is linked to strong piezomagnetism at low temperatures, we use terahertz excitation to drive a hybrid magnonphonon that is activated by a magnetic dipole moment, which is in turn coupled to a pure phonon. Both x-ray diffraction and XMCD are used to observe the dynamics of both structure and spins curing this process. In GeTe, a model ferroelectric system, we use a combination of x-ray diffraction and x-ray spectroscopy at the Ge K-edge to characterize the long- and short-range order dynamics of the ferroelecrtric soft mode across the phase transition to the paraelectric phase. The results indicate a widely applicable technique to study the roles of configurational and dynamic entropy in structural phase transitions.

If you would like to meet with Steven during his visit, please contact Michael Fechner.