Contribution of boundness and motion of nucleons to the EMC effect

The kinematical corrections to the structure function of nucleon in nucleus due to the boundness and motion of nucleons arise from the excitation of the doorway states for one-nucleon transfer reactions in the deep inelastic scattering on nuclei.Comment: 19 pages, 1 figure, 6 table

Two-dimensional Ising model with competing interactions and its application to clusters and arrays of π\pi-rings and adiabatic quantum computing

We study planar clusters consisting of loops including a Josephson $\pi$-junction ($\pi$-rings). Each $\pi$-ring carries a persistent current and behaves as a classical orbital moment. The type of particular state associated with the orientation of orbital moments at the cluster depends on the interaction between these orbital moments and can be easily controlled, i.e. by a bias current or by other means. We show that these systems can be described by the two-dimensional Ising model with competing nearest-neighbor and diagonal interactions and investigate the phase diagram of this model. The characteristic features of the model are analyzed based on the exact solutions for small clusters such as a 5-site square plaquette as well as on a mean-field type approach for the infinite square lattice of Ising spins. The results are compared with spin patterns obtained by Monte Carlo simulations for the 100 $\times$ 100 square lattice and with experiment. We show that the $\pi$-ring clusters may be used as a new type of superconducting memory elements. The obtained results may be verified in experiments and are applicable to adiabatic quantum computing where the states are switched adiabatically with the slow change of coupling constants.Comment: 32 pages, 22 figures, RevTe

Method for reliable realization of a varphi Josephson junction

We propose a method to realize a $\phi$ Josephson junction by combining alternating 0 and $\pi$ parts (sub junctions) with an intrinsically non-sinusoidal current-phase relation (CPR). Conditions for the realization of the $\phi$ ground state are analyzed. It is shown that taking into account the non-sinusoidal CPR for a "clean junction with a ferromagnetic (F) barrier, one can significantly enlarge the domain (regime of suitable F-layer thicknesses) of the $\phi$ ground state and make the practical realization of $\phi$ Josephson junctions feasible. Such junctions may also have two different stable solutions, such as 0 and $\pi$, 0 and $\phi$, or $\phi$ and $\pi$

Double proximity effect in hybrid planar Superconductor-(Normal metal/Ferromagnet)-Superconductor structures

We have investigated the differential resistance of hybrid planar Al-(Cu/Fe)-Al submicron bridges at low temperatures and in weak magnetic fields. The structure consists of Cu/Fe-bilayer forming a bridge between two superconducting Al-electrodes. In superconducting state of Al-electrodes, we have observed a double-peak peculiarity in differential resistance of the S-(N/F)-S structures at a bias voltage corresponding to the minigap. We claim that this effect (the doubling of the minigap) is due to an electron spin polarization in the normal metal which is induced by the ferromagnet. We have demonstrated that the double-peak peculiarity is converted to a single peak at a coercive applied field corresponding to zero magnetization of the Fe-layer

Proximity-driven source of highly spin-polarized ac current on the basis of superconductor/weak ferromagnet/superconductor voltage-biased Josephson junction

We theoretically investigate an opportunity to implement a source of highly spin-polarized ac current on the basis of superconductor/weak ferromagnet/superconductor (SFS) voltage-biased junction in the regime of essential proximity effect and calculate the current flowing through the probe electrode tunnel coupled to the ferromagnetic interlayer region. It is shown that while the polarization of the dc current component is generally small in case of weak exchange field of the ferromagnet, there is an ac component of the current in the system. This ac current is highly spin-polarized and entirely originated from the non-equilibrium proximity effect in the interlayer. The frequency of the current is controlled by the voltage applied to SFS junction. We discuss a possibility to obtain a source of coherent ac currents with a certain phase shift between them by tunnel coupling two probe electrodes at different locations of the interlayer region.Comment: 8 pages, 5 figure

Evidence for two-dimensional nucleation of superconductivity in MgB2_{2}

According to the crystal structure of MgB$_{2}$ and band structure calculations quasi-two-dimensional (2D) boron planes are responsible for the superconductivity. We report on critical fields and resistance measurements of 30 nm thick MgB$_{2}$ films grown on MgO single crystalline substrate. A linear temperature dependence of the parallel and perpendicular upper critical fields indicate a 3D-like penetration of magnetic field into the sample. Resistivity measurements, in contrast, yield a temperature dependence of fluctuation conductivity above T$_{c}$ which agrees with the Aslamazov-Larkin theory of fluctuations in 2D superconductors. We consider this finding as an experimental evidence of two-dimensional nucleation of superconductivity in MgB$_{2}$.Comment: 5 RevTex pages, 3 PostScript Figures ZIPed in archive Sidoren.zip. Submitted to EuroPhys. Lett. December 3, 200

Theory of doorway states for one-nucleon transfer reactions. II. Model-independent study of nuclear correlation effects

The correlation effects in nuclei owing to which the nuclear wave functions are different from the Slater determinants are studied on the basis of the original theory. The calculated numbers of nucleons out of the nuclear Fermi-surface are in reasonable agreement with the finding from the high-momentum components of the nucleon momentum distributions in nuclei. The problems concerning the nuclear binding energy are also discussed.Comment: 11 pages LaTeX, epsfig.sty + 1 PostScript figure. submitted to Journal of Nuclear Physic

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