Characteristic low-field magnetic response of granular superconductors (original) (raw)
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Physica C: Superconductivity, 2004
A bare three-dimensional model, in which grains are reduced to points, cannot fully account for the magnetic properties of granular superconductors. A dressed version of these network models is proposed to discuss the quantitative link between the low-field magnetic response of high-T c superconducting granular samples and the characteristic properties of Josephson junction network models. By means of dressed models, the temperature dependence of the d.c. field-cooled susceptibility of a simple three-dimensional granular system, consisting of eight grains in a cubic arrangement, is studied.
On the theory of diamagnetism in granular superconductors
1994
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
Polarization effects induced by a magnetic field in intrinsically granular superconductors
Journal of Experimental and Theoretical Physics, 2005
Based on the previously suggested model of nanoscale dislocations induced Josephson junctions and their arrays, we study the magnetic field induced electric polarization effects in intrinsically granular superconductors. In addition to a new phenomenon of chemomagnetoelectricity, the model predicts also a few other interesting effects, including charge analogues of Meissner paramagnetism (at low fields) and "fishtail" anomaly (at high fields). The conditions under which these effects can be experimentally measured in non-stoichiometric high-Tc superconductors are discussed.
2001
Despite the fact that Josephson Junction Arrays (JAA) have been actively studied for decades, they continue to contribute to the variety of intriguing and peculiar phenomena (both fundamental and important for potential applications) providing at the same time a useful tool for testing new theoretical ideas. To give just a few recent examples, it is sufficient to mention paramagnetic Meissner effect (PME) as well as the recently introduced thermophase and piezophase effects suggesting, respectively, a direct influence of a thermal gradient and an applied stress on phase difference between the adjacent grains. At the same time, an artificially prepared islands of superconducting grains, well-described by the various models of JJAs, proved useful in studying the charging effects in these systems, ranging from Coulomb blockade of Cooper pair tunneling and Bloch oscillations to propagation of quantum ballistic vortices. The present paper reviews some of the recently suggested novel effects which should manifest themselves either in weak-links-bearing superconductors or in artificially prepared JJAs. In Section 2 we consider the appearance of an electric-field induced magnetization (analog of the so-called magnetoelectric effect) in a model granular superconductor. The dual effect, that is an appearance of a magnetic field induced electric polarization is studied in Section 3. Finally, in Section 4 we discuss a possibility of two other interesting effects which are expected to occur in a granular material under mechanical loading. Specifically, we predict the existence of stress induced paramagnetic moment in zero applied magnetic field (Josephson piezomagnetism) and study its influence on a low-field magnetization (leading to a mechanically induced PME).
Bean-Livingston surface barrier and magnetic properties of granular superconductors
Physica C: Superconductivity, 1992
The magnetic flux penetration into a granular superconductor is studied, accounting for the Bean-Livingston surface barrier (BLSB). It is shown that the magnetic flux distribution is strongly affected by the BLSB in the case of large, closely packed granules. In particular, the intergranular magnetic field Ho appears to be much higher than the external field Hwhen H<Hs=2H_,2/ lg (where l s is the characteristic granular size and 2 is the London penetration depth). The effects related to the difference between H and Ho are discussed in the framework of a simplified model of a granular superconductor. The magnetic flux distribution is studied in the regular system of isotropic and anisotropic granules. The form of the Ho (H) curve is calculated for both increasing and decreasing field H. It is shown that the existence of the BLSB results in the strong hysteresis of the Ho(H) curve. The relation between these effects and the form of the magnetic field dependence of critical current in ceramic superconductors is discussed.
Ac Susceptibility in Granular Superconductors: Theory and Experiment
Physica C: Superconductivity, 2002
A phenomenological theory to describe the electromagnetic properties of granular superconductors, based on known bulk superconductors expressions and conventional Josephson's junctions tunneling currents, is presented and successfully used to fit distinct experimental results for the magnetic susceptibility χ as a function of the temperature and the applied magnetic field of rather different samples.
Superconducting phase transitions in granular systems
Physical Review B, 1974
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.
Concentric circular arrays of Josephson junctions as dressed models of granular superconductors
European Physical Journal B, 2008
An extended dressed Josephson network model is adopted to study the quantitative magnetic behaviour of three-dimensional granular systems. The model consists of a stack of collections of N concentric circular arrays of small identical Josephson junctions, each two adjacent elements of the stack being superconductively coupled by additional Josephson junctions. The low-field magnetic response of granular superconductors is simulated by means of the proposed model.