This award will support collaborative research in materials between Dr. Stephen Nagler, University of Florida and Professor Roger Cowley, Department of Physics, University of Oxford. The objective of the project is an investigation of metastable effects associated with incommensurate charge density waves in potassium blue bronzes. Metastability associated with phase transitions is a topic of broad current interest in statistical physics. The many related problems include ordering kinetics near first order phase transitions, and random field systems. Potassium blue bronze is a particularly interesting material, exhibiting non-linear conductivity, slow structural changes in response to applied fields, and defect induced irreversibility. The proposed project is an investigation of potassium blue bronze, using time-resolved-x-ray scattering. Questions to be addressed include the possible structural origins of unusual time dependent resistivities in irradiated potassium blue bronze, and the relationship of defects to the structural response to an applied electric field. Two principal experiments will be performed. In the first experiment the response of the system to an applied field at low temperatures will be examined in samples with a wide range of induced effects. In the second experiment, the same samples will be utilized to examine the possibility that the 90 K hysteresis in the resistivity is coupled to a non-equilibrium wave- vector. Measurements on a series of sample with different levels of defects induced by irradiation should provide much important information on the true role of defects and pinning in the field induced disordered state. This project will benefit from the complementary expertise of the two investigators. Dr. Nagler has extensive experience in the areas of phase transition, low dimensional non-linear and non-equilibrium systems studies by x-ray and neutron scattering. Dr. Cowley's background is in the application of neutron and x-ray scattering to the study of condensed matter, especially phase transitions.
