We investigate theoretically the interaction between integer and half-integer Josephson vortices (fluxons and semifluxons) in an annular Josephson junction. Semifluxons usually appear at the 0-π-boundary where there is a π-discontinuity of the Josephson phase. We study the simplest, but the most interesting case of one π-discontinuity in a loop, which can be created only artificially. We show that measuring the current-voltage characteristic after injection of an integer fluxon, one can determine the polarity of a semifluxon. Depending on the relative polarity of fluxon and semifluxon the static configuration may be stable or unstable, but in the dynamic state both configurations are stable. We also calculate the depinning current of N fluxons pinned by an arbitrary fractional vortex.

We calculate the tunneling conductance spectra of a ferromagnetic metal/insulator/superconductor using the Blonder-Tinkham-Klapwijk (BTK) formulation. Two possible states for the superconductor are considered with the time reversal symmetry (T ) broken, i.e., d x 2 −y 2 + is, or d x 2 −y 2 + id xy . In both cases the tunneling conductance within the gap is suppressed with the increase of the exchange interaction due to the suppression of the Andreev reflection. In the (d x 2 −y 2 + is)-wave case the peaks that exist when the ferromagnet is a normal metal in the amplitude of the s-wave component due to the bound state formation are reduced symmetrically, with the increase of the exchange field, while in the (d x 2 −y 2 + id xy )-wave case the residual density of states within the gap develops a dip around E = 0 with the increase of the exchange field. These results would be useful to discriminate between T -broken pairing states near the surface in high-T c superconductors. 74.20. z, 74.50.+r, 74.80.Fp

We present all the possible solutions of a Josephson junction with bias current and magnetic field with both inline and overlap geometry, and examine their stability. We follow the bifurcation of new solutions as we increase the junction length. The analytical results are in terms of elliptic functions for the case of inline geometry, and are in agreement with the numerical calculations, explaining also the strong hysteretic phenomena typically seen in the calculation of the maximum tunnelling current. This suggests a different experimental approach based on the use, instead of the external magnetic field, of the modulus of the elliptic function or the related quantity the total magnetic flux to avoid hysteretic behaviour and unfold the overlapping Imax (H ) curves.

We describe the dynamics of fluxons moving in a frustrated Josephson junction with p, d, and f -wave symmetry and calculate the I − V characteristics. The behavior of fluxons is quite distinct in the long and short length junction limit. For long junctions the intrinsic flux is bound at the center and the moving integer fluxon or antifluxon interacts with it only when it approaches the junction's center. For small junctions the intrinsic flux can move as a bunched type fluxon introducing additional steps in the I − V characteristics. Possible realization in quantum computation is presented.

We consider the proximity effect in multiterminal ferromagnet / superconductor (FSF) hybrid structures in which two or three electrodes are connected to a superconductor. We show that two competing effects take place in these systems: (i) pair breaking effects due to the response to the exchange field induced in the superconductor; (ii) a reduction of the superconducting order parameter at the interface that takes place already in NS junctions. We focus on this second effect that dominates if the thickness of the S layer is small enough. We consider several single-channel electrodes connected to the same site. We calculate the superconducting order parameter and the local density of state (LDOS). With two ferromagnetic electrodes connected to a superconductor we find that the superconducting order parameter in the ferromagnetic alignment is larger than the superconducting order parameter in the antiferromagnetic alignment (∆F > ∆AF), in agreement with [Eur. Phys. J. B 25, 373 (2002)]. If a third spin polarized electrode is connected to a superconductor we find that ∆F − ∆AF can change sign as the transparency of the third electrode increases. This can be understood from the fact that the superconducting order parameter is reduced if pair correlations among the ferromagnetic electrodes increase. If the two ferromagnetic electrodes are within a finite distance we find Friedel oscillations in the Gorkov function but we still obtain ∆F > ∆AF. * U.P.R. 5001 du CNRS, Laboratoire conventionné avec l'Université Joseph Fourier α