9 / 9
Page 48
conference
series
.com
Volume 3, Issue 2
ISSN: 2470-9905
Crystallography 2017
October 16-17, 2017
2
nd
International Conference on
October 16-17, 2017 | Chicago, USA
Applied Crystallography
Disentangle phonon modes using ultrafast electron diffraction and timely-resolved electron
crystallography
P
olaron transport, in which electron motion is strongly coupled to the underlying atomic lattice, is crucial to understanding
the electrical conductivity in many solids. The accompanying atomic displacements are themselves coupled through
phonons, but the specific phonon modes responsible for the dynamics of polaron motion have rarely been identified. In this
presentation, I will first give an overview on the 2.8MeV ultrafast electron diffraction instrument and the time resolved electron
crystallography method we developed at BNL, then focus on its application to understand charge, orbital and lattice coupling
and interaction in strongly correlated electron systems. A detailed example will be given on quantifying the dynamics of both
electronic and atomic motion in the LaSr
2
Mn
2
O
7
manganite. Using photoexcition to set the electronic system in motion, we
find that Jahn-Teller-like O, La/Sr, and Mn
4+
displacements dominate the lattice response and exhibit a dichotomy in behavior
overshoot-and-recovery for one sub-lattice versus normal behavior for the other. This dichotomy, attributed to slow electronic
relaxation, proves that polaron transport is a key process in doped manganites. Our technique with the access to high-order
reflections and being sensitive to phonons promises to be applicable for specifying the nature of electron-phonon coupling in
many complex materials.
Figure-1: An electron diffraction pattern of LsSr
2
Mn
2
O
7
at 77K obtained from the BNL 2.8MeV-130fs UED (Left). Schematic
of the ultrafast pump-probe approach is shown in the top panel (Right). The Bragg, orbital-ordered (OO) and charge-ordered
(CO) reflections are marked and quantified in the bottom panel.
Biography
Yimei Zhu is a Senior Physicist at Brookhaven National Laboratory (BNL) and Adjunct Professor at Columbia University and Stony Brook University. He has re-
ceived his BS from Shanghai Jiaotong University in 1982, MS and PhD from Nagoya University in 1987. He joined BNL as an Assistant Scientist in 1988, rising
through the rank to become Tenured Senior Physicist in 2002. He is the Founding Director of the Institute for Advanced Electron Microscopy and Facility Leader of
the Functional Nanomaterials at BNL. His research interests include electron crystallography of condensed matter physics of strongly correlated electron systems
and advanced electron microscopy including ultrafast microscopy instrumentation. He is an Inaugural Fellow of Microscopy Society of America, a Fellow of Amer-
ican Physical Society and a Fellow of American Association for the Advancement of Science. He has published more than 500 peer-reviewed journal articles and
delivered more than 300 invited talks at international conferences.
zhu@bnl.govYimei Zhu
Brookhaven National Laboratory, USA
Yimei Zhu, Struct Chem Crystallogr Commun, 3:2
DOI: 10.21767/2470-9905-C1-001