MSE Spring Seminar Series: Paul Evans, University of Wisconsin-Madison

Description

Optically Induced Polarization Phenomena in Complex Oxides: Surprises from Femtosecond Structural Studies

Paul Evans, University of Wisconsin-Madison

Ferroic complex oxides possess properties and phenomena that arise fundamentally from the interaction between their electronic or magnetic order on one hand and nanoscale dimensionality, electronic properties, and structural distortion on the other. Femtosecond-to-picosecond perturbations provide can enable functionalities that arise from optically induced phase transformations and can lead to far-from-equilibrium configurations that would otherwise not be accessible. Free-electron lasers and other ultrafast sources of x-ray radiation uniquely provide the means to probe the evolution of both the structure and polarization. The perturbations have particularly large effects in materials that exhibit intricate order, including those in which the ferroelectric polarization spontaneously develops a nanoscale domain pattern. I focus on our recent observations of picosecond-scale screening-induced phenomena in ferroelectric thin films and superlattices, which include phase transformations and the development of unusual polarization configurations. Observations at even shorter timescales point to the opportunity to probe how the population of specific electronic states is coupled to the development of the elastic stress. Future opportunities will arise from the study of equilibrium fluctuations and the dynamics of magnetic order, both of which will be enabled by an emerging new generation of x-ray light sources. I will also briefly discuss new approaches to crystal growth in epitaxial complex oxides that incorporate the crystallization of amorphous oxides.