Inductance Effects in Two-Dimensional Arrays of Josephson Junctions

Measurements and numerical studies of the self-induced magnetic field effects of twodimensional niobium Josephson junction arrays have been performed. Experiments focus on the dc electrical properties of these arrays and can be classified into four regimes: the superconducting state, flow-flow regime, the row-switching state, and novel resonance steps. We find that self-field effects can be modeled accurately with the inclusion of all the cell-to-cell interactions in the array. In the superconducting state, an increase of the depinning current occurs when the penetration depth in the array, is of the order of one or less. There is also evidence for a destruction of commensurate vortex states in the arrays as the depinning current becomes almost independent of the applied magnetic field. In the flux-flow regime, vortices can be modeled as massive particles due to the capacitive energy of the junctions. Self-field effects change the array flux-flow dynamics by effectively decreasing the vortex mass. When a row is switched, all of its junctions oscillate in a coherent fashion at the temperature dependent gap frequency and the vortex-as-a-particle phenomenological picture can no longer be used. This intra-row phase-locking is due to flux quantization and appears very robust with regards to self-fields. However, phase-locking between rows, inter-row phase-locking, is reduced with strong self-fields. It was also found that row-switching ordering appears to have some symmetry even in the presence of disorder. At a certain temperature, a transition from row-switched states to a resonant step occurs. This novel step is independent of temperature and seems to depend on both self-fields and the horizontal junctions for its dynamics. Thesis Supervisor: Terry P. Orlando Title: Professor of Electrical Engineering