Our group is broadly engaged in the study of the structure and dynamics of condensed matter using the techniques of x-ray and neutron scattering. For this purpose, we have both a 12kW rotating anode x-ray source and diffractometer and a 3kW source and diffractometer here at UCSD, but many of our studies require an intensity that can only be provided at synchrotron X-ray sources. For neutron scattering, large facilities are also necessary.Thus, we often travel for 3 to 5 days at a time to facilities such as the Advanced Photon Source at Argonne National Laboratory, the Advanced Light Source at Lawrence Berkeley Laboratory, The Spallation Neutron Source at Oak Ridge National Laboratory, the Manuel Lujan Neutron Scattering Facility at Los Alamos National Laboratory or the Cold Neutron Research Facility at the National Institute of Standards and Technology.
Our Research Program is centered on a few main areas:
(1) Magnetic films and nanostructures; oxide interfaces and multiferroics
We re using polarized neutron reflectivity and resonant magnetic x-ray scattering to study the details of the depth dependence of the magnetization and the lateral domain structure in the vicinity of the interfaces in compound magnetic structures. The systems being studied include ferromagnetic films deposited on antiferromagnets (so-called "exchange-bias" systems), multilayers exhibiting the giant magnetoresistance (GMR) effect or spin-valve systems, ferromagnet/semiconductor interfaces (so-called "spin injection systems"), magnetic nanodot arrays deposited on solid substrates, and hole arrays in magnetic films.
We are also using resonant magnetic x-ray scattering with coherent x-rays to observe magnetic "speckle" from spin systems, and we plan to study slow dynamics of domain walls in ordered magnetic structures and in frustrated spin systems such as spin glasses, etc. We are also planning to use resonant magnetic scattering with coherent X-rays to carry out imaging of magnetic domain structures in magnetic films using phase retrieval methods , or so-called "diffraction imaging". Eventually, we plan to carry out these experiments at the LCLS free-electron laser X-ray source at SLAC
(2) The structure and dynamics of model lipid membrane systems as biomimetic models for cellular membranes
We are studying the structure and dynamics of membranes composed of mixtures of phospholipids, sphingolipids and cholesterol, using X-ray and neutron scattering. These serve as model systems for studying the complex processes that go on in biomembranes, such as self-assembly, raft formation, membrane-protein interactions, etc.
Thus we are examining the conditions under which nano phase separation which leads to raft formation occurs, and the size and structure of the phase separated regions. We plan to study the structural effects of incorporation of nanoparticles, or external macromolecules, such as proteins, in these lipid membranes. We are also studying the dynamical fluctuations of these membranes with X-ray photon correlation spectroscopy, and grazing incidence neutron spin-echo experiments.
Left to right: Diego Zocco, Noravee Kanchanavatee, Kevin Huang (grad students), James Hamlin (postdoc), Colin McElroy (grad student), Ben White, Marc Janoschek (postdocs)