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Title:Quantum dynamics of small Josephson junctions: an application to superconductivity in granular films
Author(s):Fisher, Matthew Paul Alejandro
Doctoral Committee Chair(s):Leggett, Anthony J.
Department / Program:Physics
Subject(s):quantum dynamics
small Josephson functions
Abstract:This thesis is devoted to a study of the quantum dynamics of small Josephson junctions. Of interest are those features of the junction's behavior which depend explicitly on the quantum mechanical nature of the phase difference <1> between the superconductors. In Chapters I and IT several calculations are described which focus on the junction's DC resistance. A fully quantum mechanical Hamiltonian is employed which incorporates the dissipative effects due to the unpaired electrons by coupling to a bath of harmonic oscillators. It is shown that the model exhibits a novel zero temperature phase transition as a function of the strength of the dissipation. In the low dissipation regime the phase is free to tunnel quantum mechanically and the junction's resistance is finite; in response to an external current, tunnelling induces successive 21t phase slips leading to a finite voltage state. In contrast, in the high dissipation regime, tunnelling is suppressed and the junction behaves as a superconductor carrying current with no resistive losses. In Chapters m and N these results are applied in an attempt to explain the recent observation that in ultra-thin Sn films there is apparently a universal normal state sheet resistance above which superconductivity cannot be established. The ftlms are modelled as a random array of superconducting islands linked together by small Josephson junctions. By combining this picture with the calculations for the single junction behavior, a natural explanation for the observed data is presented. Specifically, it is demonstrated that when the sheet resistance is larger than the quantum of resistance, Rq=h/4e2 , quantum tunnelling of the phase between neighboring islands drives the film normal. This value of the universal resistance· agrees quantitatively with the experiment
Issue Date:1986
Genre:Dissertation / Thesis
Rights Information:1986 Matthew Paul Alejandro Fisher
Date Available in IDEALS:2011-06-03
Identifier in Online Catalog:978711

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