Paracoherence studies in Tl2CaBa2Cu2O8,CaLaBaCu3O7−y and CaSmBaCu3O7−y
TL;DR: In this paper, the region between Tm, the mid point of the superconducting transition, and Tco, the temperature at which the resistivity goes to zero, is called the paracofioerence region.
Abstract: In ceramic superconductors, where the intergrain coupling is weak, the phase transition at Tco corresponds to the temperature at which phase coherence occurs in all the grains. The region between Tm, the mid point of the superconducting transition, and Tco, the temperature at which the resistivity goes to zero, is called the paracofioerence region. The resistivity behaviour of single phase Tl2CaBa2Cu2O8, CaLaBaCu3O7−y and CaSmBaCu3O7−y has been studied in the above region and the results indicate that the excess conductivity varies as (T − Tco)−γ.
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TL;DR: In this paper, a model for granular superconductors consisting of an array of small superconducting particles interacting by Josephson coupling through insulating barriers is considered and the conditions for observing the phase-locking transition distinct from quasiordering within the grains are found.
Abstract: We consider a model for granular superconductors consisting of an array of small superconducting particles interacting by Josephson coupling through insulating barriers. We obtain systematically the various critical regions, critical temperature shifts, and crossover regions between zero- and 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 ${T}_{c}$ 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.
91 citations
TL;DR: The present work provides unambiguous experimental verification of theoretical predictions based on renormalization-group (RG) calculations and testifies to their correctness by demonstrating that the exponent γ of the ordered three-dimensional Heisenberg ferromagnet is not affected by the presence of quenched disorder.
Abstract: Accurate values of the asymptotic susceptibility critical exponent (\ensuremath{\gamma}), critical amplitude (\ensuremath{\Gamma}), and the leading ``correction-to-scaling'' exponents and amplitudes for quench-disordered ferromagnets have been determined for the first time through an elaborate analysis of precise and comprehensive ac susceptibility data taken on amorphous ${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{Ni}}_{80\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{B}}_{19}$${\mathrm{Si}}_{1}$(x =10, 13, and 16) alloys in the critical region. Consequently, the present work provides unambiguous experimental verification of theoretical predictions based on renormalization-group (RG) calculations, and testifies to their correctness by demonstrating that the exponent \ensuremath{\gamma} of the ordered three-dimensional Heisenberg ferromagnet is not affected by the presence of quenched disorder and that the ``frozen'' disorder plays the role of an irrelevant scaling field (in the RG sense).
39 citations
01 Jan 1990
28 citations
TL;DR: In this article, the role of disorder in X-Y ferromagnets and superconducting junction arrays has been analyzed, and it is shown that although the Harris criterion seemingly predicts that disorder is irrelevant, its application to fractal percolating clusters predicts exponent values in good agreement with experiment.
Abstract: The well-known analogies between X-Y ferromagnets and superconducting junction arrays are discussed in the light of data on critical exponents of the latter. The role of disorder is analysed. It is shown that, although the Harris criterion seemingly predicts that disorder is irrelevant, its application to fractal percolating clusters predicts exponent values in very good agreement with experiment.
27 citations