Revealing Charge, Orbital and Lattice Dynamics and Interplay in Correlated Electron Systems with Ultrafast Electrons

Speaker: Dr. Yimei Zhu (Brookhaven National Laboratory)

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, Zhu 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 Brookhaven National Laboratory. Zhu 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. The technique promises to be applicable for specifying the nature of electron-phonon coupling in many complex materials. 

Zhu is a senior physicist and group leader at Deptartment of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory. He is also an adjunct professor at Deptartment of Applied Physics and Mathematics, Columbia University, and Deptartment of Physics at SUNY Stony Brook. He is the founder of Institute for Advanced Electron Microscopy, and cofounders and Facility Leader of the Center for Functional Nanomaterials at Brookhaven National Laboratory.

His research interests include understanding structure-property relationship of strongly correlated electron systems, multiferroics and energy materials as well as advanced electron microscopy. During his career, he has served on various academic committees, and received many honors and awards. He is an iaugural fellow of Microscopy Society of America, and a Fellow of American Physical Society. Zhu has published more than 450 peer-reviewed journal articles and delivered more than 230 invited talks at international conferences and workshops. He received his BS from Shanghai Jiaotong University, China, and PhD from Nagoya University, Japan.