Study of granular two-band superconducting films: existence of a zero-temperature metallic phase (original) (raw)
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We investigate the suppression of the superconducting transition temperature due to Coulomb repulsion in granular metallic systems at large tunneling conductance between the grains, gT ≫ 1. We find the correction to the superconducting transition temperature for 3D granular samples and films. We demonstrate that depending on the parameters of superconducting grains, the corresponding granular samples can be divided into two groups: (i) the granular samples that belong to the first group may have only insulating or superconducting states at zero temperature depending on the bare intergranular tunneling conductance gT , while (ii) the granular samples that belong to the second group in addition have an intermediate metallic phase where superconductivity is suppressed while the effects of the Coulomb blockade are not yet strong.
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We consider a model for granular superconductors consisting of an array of small superconducting particles interacting by Josephson coupling through insulating barriers. %'e obtain systematically the various critical regions, critical temperature shifts, and crossover regions between zeroand three-dimensional behavior as functions of measurable sample parameters. The qualitative behavior of the system in the various regimes is analyzed and results for the specific heat and fluctuation conductivity in the Gaussian region above T, are obtained. The possibility of obtaining large critical regions is emphasized. The conditions for observing the phase-locking transition distinct from quasiordering within the grains are found. Theoretical predictions are compared with existing experimental results.
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Quantum fluctuations and dissipative phase transition in granular superconductors
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On the theory of diamagnetism in granular superconductors
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We study a highly disordered network of superconducting granules linked by weak Josephson junctions in magnetic field and develop a mean field theory for this problem. The diamagnetic response to a slow variations of magnetic field is found to be analogous to the response of a type-II superconductor with extremely strong pinning. We calculate an effective penetration depth λg and critical current jc and find that both λ −1 g suppressed by frustration. and jc are non-zero but are strongly Typeset using REVTEX 1 In the physics of type II superconductors it is common to distinguish between weakly and strongly disordered limits of the mixed state. The former case is described by the flux lattice distorted by disorder, while in the latter case the vortex loops proliferate and more adequate description is provided by the model in which the set of granules is coupled by