Current-voltage characteristics of tunnel junctions between superconductors with anisotropic pairing

Charge transfer in tunnel junctions between superconductors with anisotropic singlet pairing is considered theoretically on the basis of the Eilenberger equations for the quasiclassical Green’s functions. New singularities of the current-voltage characteristics, which are characteristic of the case of anisotropic pairing, are treated analytically assuming that the electrons reflect specularly from the boundaries of the tunnel barrier. All four contributions to the tunneling current are investigated. Two of them describe Josephson tunneling, and the other two contributions correspond to the quasiparticle current (the last term appears only for a variable voltage). Different dependences of the order parameter on the momentum directions in the interior of the superconductors and different orientations of the crystal axes relative to the junction plane are considered. The results of numerical calculations of the current-voltage characteristics for several particular cases are presented. Zh. éksp. Teor. Fiz. 111, 1120–1146 (March 1997)     

Vortex-glass phases in type-II superconductors

A review is given on the theory of vortex-glass phases in impure type-II superconductors in an external field. We begin with a brief discussion of the effects of thermal fluctuations on the spontaneously broken U(1) and translation symmetries, on the global phase diagram and on the critical behaviour. Introducing disorder we restrict ourselves to the experimentally most relevant case of weak uncorrelated randomness which is known to destroy the long-ranged translational order of the Abrikosov lattice in three dimensions. Elucidating possible residual glassy ordered phases, we distinguish between positional and phase-coherent vortex glasses. The study of the behaviour of isolated vortex lines and their generalization directed elastic manifolds in a random potential introduces further important concepts for the characterization of glasses. The discussion of elastic vortex glasses, i.e. topologically ordered dislocation-free positional glasses in two and three dimensions occupy the main part of our review. In particular, in three dimensions there exists an elastic vortex-glass phase which still shows quasi-long-range translational order: the 'Bragg glass'. It is shown that this phase is stable with respect to the formation of dislocations for intermediate fields. Preliminary results suggest that the Bragg-glass phase may not show phasecoherent vortex-glass order. The latter is expected to occur in systems with weak disorder only in higher dimensions (or for strong disorder, as the example of unscreened gauge glasses shows). We further demonstrate that the linear resistivity vanishes in the vortex-glass phase. The vortex-glass transition is studied in detail for a superconducting film in a parallel field. Finally, we review some recent developments concerning driven vortex-line lattices moving in a random environment.     

Critical behavior in type-II superconductors

The high-field critical behavior of type-II superconductors with weak disorder is dominated by the Landau levels of Cooper pairs. The macroscopic degeneracy of Landau manifolds suppresses phase coherence and eliminates the Abrikosov transition in dimensions two and three. A novel phase transition, unrelated to the conventional Abrikosov transition, is predicted to take its place. At this transition the normal state is unstable to the charge-density wave of Cooper pairs. The nature of this new state is discussed. This phase should be most readily observable in layered materials at fields > 1–10T.     

Current-voltage characteristics of quasi-one-dimensional superconductors: an S-shaped curve in the constant voltage regime

Applying a constant voltage to superconducting nanowires we find that its I-V characteristic exhibits an unusual S behavior. This behavior is the direct consequence of the dynamics of the superconducting condensate and of the existence of two different critical currents: j(c2) at which the pure superconducting state becomes unstable and j(c1)相似文献   

Ring-shaped vortex domain in type-II superconductors

We present results of experiments in superconducting niobium and numerical simulations showing the creation of a metastable ring-shaped vortex domain by heating. Such vortex rings, if pinned by structural defects, can exist forever.     

Extension of Eliashberg's theory to type-II superconductors

Eliashberg's theory is extended to type-II superconductors in such a way that band structure effects and anisotropies of the phonon-induced electron-electron interaction are included. Thermodynamic potentials for the superconducting system are presented.     

Autowave dynamics of the magnetic flux in nonideal type-II superconductors with different current-voltage characteristics

An analysis was performed of the processes of penetration of a macroscopic electromagnetic field into superconducting media with different current-voltage characteristics induced by a variable external magnetic field or by carrier transport. It has been shown that even if a finite electrical voltage arises in the superconductor before the critical current is reached, the magnetic flux, as in the critical state model, penetrates into the superconductor at a finite rate as a characteristic electromagnetic wave. At its front, a special condition is fulfilled; namely, a smooth transition to the nonperturbed value of the strength of the electric field induced by an external perturbation. Formulas are given for the calculation of the penetration rate of the electromagnetic field into a superconductor. For corroboration of the formulated relationships, the study was compared with corresponding numerical calculations.     

Vortex washboard voltage noise in type-II superconductors

In order to characterize flux flow through disordered type-II superconductors, we investigate the effects of columnar and point defects on the vortex velocity/voltage power spectrum in the driven non-equilibrium steady state. We employ three-dimensional Metropolis Monte Carlo simulations to measure relevant physical observables including the force-velocity/current-voltage (I-V) characteristics, vortex spatial arrangement and structure factor, and mean flux line radius of gyration.Our simulation results compare well to earlier findings and physical intuition.We focus specifically on the voltage noise power spectra in conjunction with the vortex structure factor in the presence of weak columnar and point pinning centers. We investigate the vortex washboard noise peak and associated higher harmonics,and show that the intensity ratios of the washboard harmonics are determined bythe strength of the material defects rather than the type of pins present.Through varying columnar defect lengths and pinning strengths as well as magnetic flux density we further explore the effect of the material defects on vortex transport.It is demonstrated that the radius of gyration displays quantitatively uniquefeatures that depend characteristically on the type of material defects presentin the sample.