“Revealing Charge, Orbital and Lattice Dynamics and Interplay in Correlated Electron Systems with Ultrafast Electrons”
Ultrafast electron diffraction and microscopy, taking advantage of the large interaction cross-sections of electrons with matter, have been identified as one of the frontiers and future directions of modern electron microscopy. In this presentation, I will first give an overview of the field as well as a brief introduction to the 2.8MeV-130fs ultrafast electron diffraction system we recently developed at BNL. I will then focus on its applications to understand charge density waves and charge, orbital and lattice coupling in strongly correlated electron systems. Detailed examples, including LaSr2Mn2O7 manganite, will be given on quantifying the dynamics of both electronic and atomic motion. Using photoexcition to set the electronic system in motion, we find that Jahn-Teller-like O, La/Sr, and Mn4+ phonon modes dominate the lattice response and exhibit a dichotomy in behavior. This dichotomy, attributed to slow electronic relaxation, proves that polaron transport is a key process in doped manganites. Our technique promises to be applicable for specifying the nature of electron-phonon coupling in many complex materials.