Quantum effects and the resistive transition in superconducting granular films |
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Authors: | W Zwerger |
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Affiliation: | (1) Physik-Department, Technische Universität München, Garching, West Germany |
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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 atT=0 is possible only if the normal-state film resistanceR
n
is smaller than a critical valueR
n
c
which depends only logarithmically on the Josephson coupling and charging energies. The particular valueR
n
c
=6.5 k 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 aboveT
c are determined. The resulting precursor conductivity does not explain the observed exponential decrease withR
n-R
n
c
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. |
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Keywords: | |
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