Quantum effects and the resistive transition in superconducting granular films

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Abstract

Static and dynamic properties of an array of Josephson junctions shunted by Ohmic resistors are discussed within a quantum Ginzburg-Landau theory. The phase diagram at zero temperature is calculated in mean field approximation. It shows that global superconductivity at T=0 is possible only if the normal-state film resistance Rn is smaller than a critical value Rnc which depends only logarithmically on the Josephson coupling and charging energies. The particular value Rnc=6.5 kΩ found in recent experiments on granular films is in reasonable agreement with estimates for these parameters. A phenomenological order parameter relaxation mechanism is introduced and the associated fluctuation-induced conductivity and diamagnetic susceptibility above Tc are determined. The resulting precursor conductivity does not explain the observed exponential decrease with Rn-Rnc of the residual resistance at low temperature. However, a very simple model for the resistance due to vortex flow, generalizing the classical Kosterlitz-Thousless picture, is in good agreement with the experimental data.

Original languageEnglish
Pages (from-to)291-318
Number of pages28
JournalJournal of Low Temperature Physics
Volume72
Issue number3-4
DOIs
StatePublished - Aug 1988

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