General Relativistic Thermoelectric Effects in Superconductors

We discuss the general-relativistic contributions to occur in the electromagnetic properties of a superconductor with a heat flow. The appearance of general-relativistic contribution to the magnetic flux through a superconducting thermoelectric bimetallic circuit is shown. A response of the Josephson junctions to a heat flow is investigated in the general-relativistic framework. Some gravitothermoelectric effects which are observable in the superconducting state in the Earth's gravitational field are considered.Comment: 13 pages, 2 figure

The current-phase relation in Josephson tunnel junctions

The $J(\phi)$ relation in SFIFS, SNINS and SIS tunnel junctions is studied. The method for analytical solution of linearized Usadel equations has been developed and applied to these structures. It is shown that the Josephson current across the structure has the sum of $\sin \phi$ and $\sin 2\phi$ components. Two different physical mechanisms are responsible for the sign of $\sin 2\phi$. The first one is the depairing by current which contributes positively to the $\sin 2\phi$ term, while the second one is the finite transparency of SF or SN interfaces which provides the negative contribution. In SFIFS junctions, where the first harmonic vanishes at 0 - $\pi$ transition, the calculated second harmonic fully determines the $J(\phi)$ curve.Comment: 6 pages, 2 figure

Re-entrant superconductivity in Nb/Cu(1-x)Ni(x) bilayers

We report on the first observation of a pronounced re-entrant superconductivity phenomenon in superconductor/ferromagnetic layered systems. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu(1-x)Ni(x). The superconducting transition temperature T_{c} drops sharply with increasing thickness d_{CuNi} of the ferromagnetic layer, until complete suppression of superconductivity is observed at d_{CuNi}= 4 nm. Increasing the Cu(1-x)Ni(x) layer thickness further, superconductivity reappears at d_{CuNi}=13 nm. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one dimensional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state in the ferromagnetic layer.Comment: 3 pages, 3 figures, REVTEX4/twocolum

Ground state and bias current induced rearrangement of semifluxons in 0-pi long Josephson junctions

We investigate numerically a long Josephson junction with several phase pi-discontinuity points. Such junctions are usually fabricated as a ramp between an anisotropic cuprate superconductor like YBCO and an isotropic metal superconductor like Nb. From the top, they look like zigzags with pi-jumps of the Josephson phase at the corners. These pi-jumps, at certain conditions, lead to the formation of half-integer flux quanta, which we call semifluxons (SF), pinned at the corners. We show (a) that the spontaneous formation of SFs depends on the junction length, (b) that the ground state without SFs can be converted to a state with SFs by applying a bias current, (c) that the SF configuration can be rearranged by the bias current. All these effects can be observed using a SQUID microscope.Comment: ~8 pages, 6 figures, submitted to PR

Superconducting decay length in a ferromagnetic metal

The complex decay length xi characterizing penetration of superconducting correlations into a ferromagnet due to the proximity effect is studied theoretically in the frame of the linearized Eilenberger equations. The real part xi_1 and imaginary part xi_2 of the decay length are calculated as functions of exchange energy and the rates of ordinary, spin flip and spin orbit electronic scattering in a ferromagnet. The lengths xi_1,2 determine the spatial scales of, respectively, decay and oscillation of a critical current in SFS Josephson junctions in the limit of large distance between superconducting electrodes. The developed theory provides the criteria of applicability of the expressions for xi_1 and xi_2 in the dirty and the clean limits which are commonly used in the analysis of SF hybrid structures.Comment: 5 pages, 3 figure

On Field Induced Diaelastic Effect in a Small Josephson Contact

An analog of the diaelastic effect is predicted to occur in a small Josephson contact with Josephson vortices manifesting itself as magnetic field induced softening of the contact shear modulus C(T,H). In addition to Fraunhofer type field oscillations, C(T,H) is found to exhibit pronounced flux driven temperature oscillations near T_C

Spontaneous Spin Polarized Currents in Superconductor-Ferromagnetic Metal Heterostructures

We study a simple microscopic model for thin, ferromagnetic, metallic layers on semi-infinite bulk superconductor. We find that for certain values of the exchange spliting, on the ferromagnetic side, the ground states of such structures feature spontaneously induced spin polarized currents. Using a mean-field theory, which is selfconsistent with respect to the pairing amplitude $\chi$, spin polarization $\vec{m}$ and the spontaneous current $\vec{j}_s$, we show that not only there are Andreev bound states in the ferromagnet but when their energies $E_n$ are near zero they support spontaneous currents parallel to the ferromagnetic-superconducting interface. Moreover, we demonstrate that the spin-polarization of these currents depends sensitively on the band filling.Comment: 4 pages, 5 Postscript figures (included

RF assisted switching in magnetic Josephson junctions

We test the effect of an external RF field on the switching processes of magnetic Josephson junctions (MJJs) suitable for the realization of fast, scalable cryogenic memories compatible with Single Flux Quantum logic. We show that the combined application of microwaves and magnetic field pulses can improve the performances of the device, increasing the separation between the critical current levels corresponding to logical "0" and "1." The enhancement of the current level separation can be as high as 80% using an optimal set of parameters. We demonstrate that external RF fields can be used as an additional tool to manipulate the memory states, and we expect that this approach may lead to the development of new methods of selecting MJJs and manipulating their states in memory arrays for various applications

Josephson effect in double-barrier superconductor-ferromagnet junctions

We study the Josephson effect in ballistic double-barrier SIFIS planar junctions, consisting of bulk superconductors (S), a clean metallic ferromagnet (F), and insulating interfaces (I). We solve the scattering problem based on the Bogoliubov--de Gennes equations and derive a general expression for the dc Josephson current, valid for arbitrary interfacial transparency and Fermi wave vectors mismatch (FWVM). We consider the coherent regime in which quasiparticle transmission resonances contribute significantly to the Andreev process. The Josephson current is calculated for various parameters of the junction, and the influence of both interfacial transparency and FWVM is analyzed. For thin layers of strong ferromagnet and finite interfacial transparency, we find that coherent (geometrical) oscillations of the maximum Josephson current are superimposed on the oscillations related to the crossover between 0 and $\pi$ states. For the same case we find that the temperature-induced $0-\pi$ transition occurs if the junction is very close to the crossovers at zero temperature.Comment: 13 pages, 6 figure