Dressed Josephson junction network models and low-field magnetic response of high-Tc granular superconductors (original) (raw)
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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.
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).
Characteristic low-field magnetic response of granular superconductors
Physica C: …, 1998
The low-field magnetic response of a physical system consisting of eight superconducting spherical grains in a cubic arrangement is studied by means of a three-dimensional Josephson junction network. The lower threshold field for this ™ system is numerically studied as a function of the inclination of the externally applied magnetic field H with respect to the z-axis. q 1998 Published by Elsevier Science B.V. All rights reserved. PACS: 74.80.B; 74.25.Ha; 74.50.q r
Modelling of high-Tc superconductors by means of disordered Josephson-junction arrays
Journal of the Less Common Metals, 1990
A simple model is presented for attempting to reproduce the magnetic response of high-T, granular superconductors to an applied magnetic field. A "sample" is assumed to be composed by 2D array of superconducting grains interacting via Josephson or proximity-effect coupling. We studied the influence of an external magnetic field acting upon the sample. Its ground-state properties, that is, the zero-temperature properties, are examined. In particular we report on the behaviour of the magnetic moment with the field, for different "disordered" samples. We considered both the disorder due to a random distribution of the grain positions and to the bond dilution (always beyond the percolation threshold). This latter is by far more effective, and causes a shrinkage to occur in the butterfly-like hystheresis cycle. It allows, furthermore, to approach through a different way the question of whether a percolative transition of the junction ensemble takes place. The hystheretic effects are only seen when the field is increased beyond a certain critical value, because of vortices in the wave-function phase penetrating into the system. Such vortices are pinned near the defects.
Thermal expansion of granular superconductors based on elastic response of Josephson junction arrays
Journal of Physics: Conference Series, 2008
We introduce the concept of thermal expansion (TE) in Josephson systems as an elastic response to an effective stress field. The temperature and magnetic field dependences of TE coefficient can be studied both analytically and numerically in a single junction and in a square array of Josephson junctions (JJA) [1]. We found that in addition to field oscillations due to Fraunhofer-type dependence of the critical current, both single junction and JJAs may exhibit flux driven temperature oscillations of the TE coefficient near T c provided the applied magnetic field is strong enough to compensate for the screening-induced effects. We briefly discuss possible consequences of TE coefficient temperature oscillations for the local penetration of magnetic field in granular systems modelled as JJAs.
Journal of Experimental and Theoretical Physics Letters, 2002
The temperature and electric field dependence of electronic contribution to the thermal conductivity (TC) of a granular superconductor is considered within a 3D model of inductive Josephson junction arrays. In addition to a low-temperature maximum of zero-field TC κ(T, 0) (controlled by mutual inductance L0 and normal state resistivity Rn), the model predicts two major effects in applied electric field: (i) decrease of the linear TC, and (ii) giant enhancement of the nonlinear (i.e. ∇T -dependent) TC with ∆κ(T, E)/κ(T, 0) reaching 500% for parallel electric fields E ≃ ET (ET = S0|∇T | is an "intrinsic" thermoelectric field). A possiblity of experimental observation of the predicted effects in granular superconductors is discussed. PACS: 74.25.Fy, 74.50.+r, 74.80.Bj 1. Introduction. Inspired by new possibilities offered by the cutting-edge nanotechnologies, the experimental and theoretical physics of increasingly sophisticated mesoscopic quantum devices (heavily based on Josephson junctions and their arrays) is becoming one of the most exciting and rapidly growing areas of modern science . In addition to the traditional fields of expertise (such as granular superconductors [2]), Josephson junction arrays (JJAs) are actively used for testing principally novel ideas (like, e.g., topologically protected quantum bits [3]) in a bid to solve probably one of the most challenging problems in quantum computing. Though traditionally, the main emphasis in studying JJAs has been on their behavior in applied magnetic fields, since recently a special attention has been given to the so-called electric field effects (FEs) in JJs and granular superconductors . The unusually strong FEs observed in bulk high-T c superconducting (HTS) ceramics [4] (including a substantial enhancement of the critical current, reaching ∆I c (E)/I c (0) = 100% for E = 10 7 V /m) have been attributed to a crucial modification of the original weaklinks structure under the influence of very strong electric fields. This hypothesis has been corroborated by further investigations, both experimental (through observation of the correlation between the critical current behavior and type of weak links [5]) and theoretical (by studying the FEs in SN S-type structures [6] and d-wave granular superconductors ). Among other interesting field induced effects, one can mention the FE-based Josephson transistor and Josephson analog of the magnetoelectric effect [9] (electric field generation of Josephson magnetic moment in zero magnetic field). At the same time, very little is known about influence of electric fields on
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.