Ultrafast structural dynamics observed with atomic scale resolution

Note: Pizza served at 11:45 AM
Speaker: Nuh Gedik, MIT

When: October 24, 2008 (Fri), 12:00PM to 01:00PM (add to my calendar)
Location: SCI 352

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract:
Ultrafast optical spectroscopy has long been used with great success
to generate and probe non-equilibrium electronic excitations with
femtosecond time resolution. The spatial resolution in these
techniques, however, is limited to micron scales and structural
dynamics can only be inferred indirectly. I will report direct
measurements of structural dynamics with atomic scale spatial
resolution by using ultrafast electron diffraction (UED). In UED, a
femtosecond laser pulse is split into two, the first part is used to
induce structural change and the second part is used to generate
ultrafast high energy electron packets via photoelectric effect.
Recording the diffraction pattern of these electron packets at
different times after the photo-excitation of the sample provides a
movie of the laser induced structural change with sub-picosecond
temporal and sub-Angstrom spatial resolution. I will discuss recent
experiments where we used UED to observe lattice dynamics in cuprate
superconductors in response to photo-excitation of the charge
carriers. Above certain threshold laser intensity, we observe direct
conversion between two structures with different c axis lattice
constants indicating a non-equilibrium structural phase transition.