Vortex Motion and Dynamical States in Josephson Arrays

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w:\awards\awards96\num.doc 9610042 Orlando This experimental research project focuses on the physics, dynamical excitations, and potential applications of arrays of Josephson junctions, devices which nonlinearly interact. Three areas are to be studied: (1) Novel and universal dynamical states, including a fully frustrated array with junctions along every branch, where the dynamics can be reduced to three dynamical variables. (2) Inductively coupled arrays, which form a model system for coupled layers of high-temperature superconductors and for coupled systems of nonlinear oscillators. (3) Flux-flow in 2-d arrays will provide a model system for investigating the similar vortex dynamics that occurs in thin films of high temperature superconductors. The study of vortex motion in this system will clarify aspects of pendula-like whirling modes in discrete systems. Other dynamical states corresponding to local and global phase-locking mechanisms will be also be studied. The research is characterized by integration of experiment, numerical simulation, and mathematical analysis, and will exploit existing commercial foundry service for fabrication of arrays of Josephson junctions. %%% This experimental research project is in the types of "motions" or excitations that can exist in a two-dimensional array of non- linearly interacting systems (Josephson junctions). One example of an excitation is a magnetic flux quantum (vortex) trapped within a closed loop through which a supercurrent flows. Such vortices can move about the lattice, and can also interact with other vortices which simultaneously exist. The mathematical equations describing such systems are non-linear and can have singular solutions called solitons, in which considerable interest exists in other areas of science. In fact, the project to be carried out in major parts will attempt to model the behavior of other systems of interest, including aspects of the motion of magnetic flux in high temperature superconductors. The researchers will combine experimental measurements with numerical simulations and with more conventional analytical mathematics to understand the observed behavior, which may have implications on additional systems than the systems specifically at hand. In one of its aspects the array of Josephson junctions may have applications in detecting and in generating microwave radiation, which will also be of interest in this project. Results from this research may include unusual new effects or devices which may find new application in technology. This research project is interdisciplinary in nature and involves graduate students who will be excellently trained to enter positions in industry, government or education. The project will also foster inclusion of women and under-represented groups into the national scientific work force. ***