Theoretical Studies of Josephson Arrays, High-Temperature Superconductors, and Inhomogeneous Media

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0104987StroudTheoretical research will be conducted in three areas of materials research: (1) the physics of superconducting arrays and related materials: (2) fluctuations and inhomogeneities in cuprate-based high temperature superconductors; (3) linear and nonlinear response of macroscopically inhomogeneous materials. Superconducting arrays are arrangements of superconductors which are weakly coupled together by Josephson or proximity-effect interactions. They have a wide variety of potential applications and are also good models for superconducting thin films. In this area continued study of underdamped Josephson arrays coupled to a resonant cavity will be carried out. In addition, a study of noise produced by magnetic flux motion in arrays and films will also be undertaken, as well as a study of conditions under which a superconducting array can lock into a coherent state. Finally, a study will be made of quantum effects in superconducting arrays, films and smaller groups of junctions. Models for terahertz absorption in the underdoped high temperature superconducting materials will be studied. Also to be investigated are models of low-angle grain boundaries in the ab-planes of the high temperature superconductors, since grain boundaries limit the critical current. The c-axis current-voltage characteristics of these materials will also be investigated, as well as the conditions governing the position and width of the Josephson plasmon resonance in the most anisotropic materials. Also, recent calculations o fquantum melting of the vortex lattice at zero temperature will be compared to experiment. The PI will also extend recent work on macroscopically inhomogeneous media to the study of magnetic composites. Here the problems to be addressed include magnetoresistance arising from the inhomogeneous conductivity tensor in a material with a ferromagnetic domain structure, and the behavior of magnetic multilayers coupled through nonmagnetic layers, which will be studied by a model analogous to the Lawrence-Doniach treatment of layered superconductors. Finally, the PI will study the electromagnetic response of collections of small metal and dielectric particles contained in an optical microcavity.The research involves studies of several fundamental questions in condensed matter physics, and may lead to a wide variety of technological applications. It will also contribute to human resources in science and technology by training graduate students and postdoctoral fellows.%%%Theoretical research will be conducted in three areas of materials research: (1) the physics of superconducting arrays and related materials: (2) fluctuations and inhomogeneities in cuprate-based high temperature superconductors; (3) linear and nonlinear response of macroscopically inhomogeneous materials. The research involves studies of several fundamental questions in condensed matter physics, and may lead to a wide variety of technological applications. It will also contribute to human resources in science and technology by training graduate students and postdoctoral fellows.***