[en] Short communication

No abstract available

[en] We have performed a linear stability analysis of two arrays of resistively shunted Josephson junctions: a ladder array and a so-called modified linear array. We find the periodic solutions to be linearly stable for a wide range of bias currents in the absence of a load. This is contrasted with the well-studied globally coupled linear array, where stability of the periodic solutions is a sensitive function of bias current and load parameters. For the ladder array, we have studied the nature of the mesh currents for the different decay modes. Numerical evidence leads us to conclude that the branches of the ladder parallel to the bias current play an important role in helping to damp out perturbed currents. We also compare the long-time dynamics of these Josephson-junction arrays with that of an RL network, which is a ladder of resistors and inductors, and for which the decay rates and mesh currents are calculated exactly. We find that at long times the dynamics of all three arrays are basically identical. copyright 1998 The American Physical Society

No abstract available

[en] Critical current of inhomogeneous intergranular Josephson transition is calculated in the assumption concerning superconductivity suppression by local strains of boundary dislocations with random distribution

[en] The experimental demonstration of the Josephson effect is a direct manifestation of the quantum phase of the superconductive order parameter and of the coupling of this phase to the electromagnetic field. The ac Josephson effect links the time evolution of the phase difference between two superconductors to the voltage between them. When this voltage is kept fixed externally, the phase difference increases linearly with time, giving rise to an oscillating supercurrent between the superconductors if they are coupled by a weak link such as a tunnel barrier. This effect depends only on the bose like character of the particles carrying the supercurrent. It was thus important to test if the Josephson effect could be observed with copper oxide based superconductors. This was achieved by our experiment performed at Saclay and by other experiments conducted independently. We will focus in this paper on our latest results and their discussion

[en] The possibility of the occurrence of Josephson and flux-flow effects in microbridges, being manufactured from a type I superconductor and having got dimensions that are larger than the coherence length of the superconducting material is investigated. On account of theoretical considerations the Josephson effect as well as the existence of individual flux quanta should not be possible in such geometries, but exceeding of the critical current should be characterized by formation and motion of flux tubes containing a multitude of flux quanta. Based on earlier work, it could be shown at first by using different techniques of sample preparation and manipulation that the effects shown there have to be explained to a large extent by an intermediate layer in the samples caused by the manufacture process. If the bridge has got small dimensions (10-20 μm of width) formation of a Josephson element may be possible also in the range of the bridge. The sample characteristic depending on the high-frequency current applied for demonstration and on temperature, one has to assume that the high-frequency current makes the total region of the bridge normally conductive, a SNS contact thus being formed. The RSJ model as well as the characteristic-forming mechanisms described from it are discussed in detail by means of the results of an electronic Josephson effect-simulating device constructed within the scope of this work. (orig./HP)

[en] The Josephson effect describes the coherent coupling between superconductors and the resulting supercurrent. Microscopically, it arises from the existence of discrete quasiparticle states, localized at the weak link, the Andreev bound states. They come in doublets in each conduction channel of the weak link, with energies symmetric about the Fermi energy and opposite supercurrents. Each Andreev doublet gives rise to four states: the ground state |-> and the excited state |+>, with even parity, and the excited odd states |↑> and |↓>. Is it possible to address and control Andreev doublets? This thesis describes two sets of experiments designed to answer this question using the most basic Josephson element, a one-atom contact between two superconducting electrodes. In a first experiment, we have observed and characterized the excited odd states |↑> and |↓>. As expected for a spin-degenerate system, they do not carry supercurrent. In this experiment the excitation was uncontrolled and resulted from trapping of spurious quasiparticles. We have measured the lifetime of the odd states: under some condition, it is found to exceed 100 μs. The second experiment is a photon-absorption spectroscopy of the Andreev doublet. It was performed by using a Josephson junction as an integrated on-chip microwave emitter and detector. The observed Andreev transitions correspond to excitation from the ground state |->to the excited even state |+>, and are well accounted for by our quantum model. This result opens the way to coherent manipulation of this two level system. The direct observation of the excited Andreev state, either by quasiparticle-injection or photon-absorption, strongly supports the mesoscopic theory of the Josephson effect. It shows that in addition to the phase difference, each channel of a Josephson weak link possesses an internal fermionic degree of freedom. It could be used to code information in a novel type of superconducting qubit. (author)

[en] We demonstrate that the well known phase-locking mechanism leading to Shapiro steps in ac-driven Josephson junctions is always accompanied by a higher-order phase-locking mechanism similar to that of the parametrically driven pendulum. This effect, resulting in a π-periodic effective potential for the phase, manifests itself clearly in the parameter regions where the usual Shapiro steps are expected to vanish. copyright 1999 The American Physical Society

[en] A multi-chip 10 V programmable Josephson voltage standard (PJVS) system was demonstrated using a closed-cycle refrigerator. We precisely measured the PJVS by a direct comparison measurement with a conventional Josephson voltage standard. The result agreed within a combined standard uncertainty of 3.9 x 10^-10 at 10 V.