Dynamics of Condensed Matter Systems

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My research concentrates on the time evolution of microstructures. Since the microstructure depends on the history of the sample it requires nonequilibrium thermodynamics for its understanding. The microstructure of a material is central to most of its physical and mechanical properties. Not only failure rates, but many other important properties including tensile strength, chemical reactivity and magnetic coercivity, depend crucially on this morphology. The typical length scales of these structures is micrometers. Many of the advanced materials, often denoted as ``modern space age'' materials, obtain their properties from controlling their microstructure by careful and sophisticated processing techniques. It is an important fundamental problem in physics to understand how microstructures arise, how to characterize them, how they evolve in time and ideally to control them. The nature and role of coherence and correlations in disordered systems is still not fully understood. Real-time in-situ diffraction measurements, using either time resolved diffraction or x-ray photon correlation spectroscopy, allow measurements of the microstructure under conditions similar to conventional processing and therefore are ideally suited for these studies. Two main areas of development are better instrumentation and techniques for in-situ time-resolved scattering to help address these issues and to better understand the physics described above using them. It is my opinion is that one of the largest impacts of physics has been to develop the instrumentation used by the rest of science. In order to pursue this objective, I am involved in designing and building instrumentation to use the brightest x-ray synchrotron sources and the new x-ray laser at SLAC. The newest project is a new time-resolved femtosecond electron diffraction setup. This is in collaboration with B. Siwick and D. Cooke, both faculty at McGill. This emphasis has allowed us to measure materials while the system is being taken out of equilibrium and as it approaches the new equilibrium or metastable state. Besides continuing my current research, a new project is a collaboration with the Prof. Siwick to perform ultrafast electron diffraction (UED). A first set of materials are charge density wave systems (NbSe2, TiSe2, TaSe2 and TaS2) where optical excitations couple to the electron and phonon dynamics. The ability to measure the structures with sub-picosecond time scales is needed o study these effects