1,721,195 research outputs found
Displaced linear slope and fluxon dynamics in large one-dimensional Josephson junctions
No full textA displaced linear slope (DLS) appears under particular conditions in the current-voltage characteristic of large Josephson tunnel junctions. The significant features that enable one to distinguish the DLS from other structures in theI–V characteristic are discussed. The experimental magnetic field behavior and the temperature dependence of the DLS in different geometrical configurations (cross, in-line, and overlap) are reported; a very consistent behavior has been found for all geometries. Different dynamical states of the junction as a function of both the external magnetic field and the bias current are analyzed. Possible explanations of the DLS in terms of the motion of flux quanta inside the junction are discussed
An approximate analysis of the I-V characteristic of zero field singularities in long Josephson junction
No full textFluxon propagation in long overlap Josephson junctions in the presence of losses and bias is analyzed. It is shown that losses determine a lower limit of the fluxon contraction. For a linear loss analytical expressions for the energy, the momentum, and the current-voltage relation are given
Diamagnetic response of a very simple superconducting granular system
No full textThe diamagnetic response of superconducting granular systems is studied by means of a network of Josephson junctions (JJs) and inductances. We study the diamagnetic properties of the simplest possible granular superconductor: a three-grain system which reduces to a superconducting loop closed by three JJs. We numerically determine: the irreversibility line of the system in the H vs T plane and the temperature dependent lower threshold field Hgc1(T). In addition, we remark that the metastable shielding states realized above a thermal activation line in the H vs T diagram decay in experimentally detectable times toward thermodynamic equilibrium. Finally, we mention how this simple model can be extended to more complex systems. © 1991
Irreversible low field flux penetration in sintered superconducting systems
No full textThe irreversible low field magnetic flux penetration in granular superconductors is analyzed by means of a 2D network of Josephson junctions under the conditions of strong grain coupling and non-negligible intergranular regions. Analytical results on simple systems and numerical simulations show that the first penetration critical field is determined by the shielding currents crossing through the junctions. These currents reduce the Josephson potential barriers and cause the instability of the magnetic metastable states. We show that by this approach a critical state model can be derived
Hysteretic effects in the D.C. current-voltage characteristic of normal Nb/Pb tunnel junctions
No full textA new method to detect the vortex glass phase and its evidence in YBCO
No full textThe evidence of the vortex glass phase has been obtained by analysing the nonlinear magnetic response of type-II superconductors. The method introduced here is based on a combined frequency dependence analysis of the real and imaginary part of the 1st and 3rd harmonics of the AC magnetic susceptibility. The analysis has been performed by taking into account both the components and the Cole-Cole plots (i.e. the imaginary part as a function of the real part). Numerical simulations have been used to identify the fingerprints of the magnetic behaviour in the vortex glass phase. These characteristics allowed the vortex glass phase to be distinguished from the other disordered phases, even those showing similar electrical properties. Finally, this method has been successfully applied to detecting the vortex glass phase in an YBCO bulk melt-textured sample
Harmonics of the AC susceptibility for the study of I-V curves in melt grown YBCO
No full textThe measurements of the first and the third harmonics of the AC magnetic susceptibility, performed on melt grown YBCO samples as a function of the temperature and the external parameters (frequency and amplitude of AC magnetic field, intensity of a DC field) were studied by using the Cole–Cole plot analysis. By considering the AC field dependence of the third harmonics Cole–Cole plots, we have extracted information about the peculiar behaviour of the I–V characteristics and, therefore, about the dissipative phenomena in the sample. The experimental results have been analysed with the help of both analytical and numerical curves. In particular, the use of a phenomenological expression for the resistivity allowed us to reproduce the main experimental features, including the observed invariance of the area inside the Cole–Cole plots and their behaviour as a function of the AC field
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