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Title:Phase dynamics and magnetic field response of proximity-coupled superconductor arrays
Author(s):Springer, Kendall Norris
Doctoral Committee Chair(s):Van Harlingen, Dale J.
Department / Program:Physics
Subject(s):phase dynamics
magnetic field response
proximity-coupled superconductor arrays
electrical transport properties
Abstract:We have fabricated and measured electrical transport properties of arrays of proximity-coupled superconductor islands as a function of temperature, magnetic field, and bias current for several geometries. The weakly-coupled arrays, a physical realization of the frustrated XYmodel, show interesting behavior relating to phase coherence, fluctuations, and dynamics. Our samples display a broad transition to zero-resistance at a field-dependent temperature Te(H). Present theories explain the transition at Te (in zero field) as an unbinding of pairs of opposite-polarity vortices --topological excitations in the phase of the order-parameter. Above Te the free vortices give rise to a d.c. voltage --and therefore resistance --in the presence of a current bias. The theoretical picture is less clear in the presence of. a magnetic field, where a background lattice of vortices adds frustration and the possibility of additional types of excitations. We observe minima (subminima) in the voltage V(H) at those fields producing a flux lattice (superlattice) approximately commensurate with the array. Reduction of the bias current produces additional such structure indicating an increase in the effective range of phase coherence. Further reduction of the bias gives rise to a seemingly random but reproducible V-vs.-H "fingerprint" of disorder in the array. Measurements on two-unit-cell periodic "checkerboard" and quasiperiodic Penrose arrays distinguish structure arising due to the irrational cell area ratios from that due to iii fluxoid quantization over larger areas. The power-law dependence of the current-voltage characteristics as a function of temperature for the Penrose is generally consistent with the predictions for a KosterlitzThouless transition at zero applied field, but show more complex behavior at finite fields. In square arrays we find the voltage noise follows V(H) at low bias currents, but shows peaks at the voltage minima at higher bias levels, suggesting current-induced unbinding of Ising-domainwall excitations separating regions of different chirality at commensurate applied fields. Computer simulations of the time-stepped Resistively-Shunted-Junction equations for small arrays are discussed.
Issue Date:1988
Genre:Dissertation / Thesis
Rights Information:1988 Kendall Norris Springer
Date Available in IDEALS:2011-05-17
Identifier in Online Catalog:3476311

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