Dynamics of Optically Induced Transformations in Complex Oxide Electronic Materials

The conventional approach to developing an understanding of the electronic and magnetic properties of complex oxides has been to adjust their chemical composition, to impose elastic constraints, and to create nanoscale interfaces. It has recently become increasingly possible to supplement this conventional approach by using strategies that drive electronic materials into states far from equilibrium using ultrafast optical excitation. States reached by the electronic or elastic perturbation resulting from optical excitation have a challenging range of characteristic times. At the shortest times, the characteristic effects occur at the sub- or single-digit picoseconds â€" an excellent match for emerging free-electron-laser-based x-ray characterization techniques. Examples of the perturbation induced by optical excitation include the reorganization and reconfiguration of ferroelectric polarization in thin films and superlattices and strain-induced perturbation of structural order. The stress producing these phenomena arises at the sub-picosecond timescale and provides insight into how electronic excitation is linked to structural distortion. In addition, the elastically induced reorientation of oxygen octahedral rotation in BiFeO3 holds the possibility of using optical pulses to modify phenomena such as superexchange that are linked to structural order. The results also define the limits of x-ray fluences before x-ray-induced chemical and structural effects arise. Future prospects hold the possibility that the magnetic dynamics, including magnon-elastic coupling can be understood and exploited using this approach.

Speaker: Paul Evans, Johns Hopkins University