The influence of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/d-wave superconductor contact

The influence of phase shifts of electron waves passing through and reflected by the potential barrier on the Andreev reflection in a ferromagnet/isolator/d-wave superconductor (FIS) contact is studied. It is found that in a superconductor the surface spin-dependent Andreev bound states inside the superconducting gap are formed as a result of the interference of electron-like and hole-like quasiparticles due to repeated Andreev reflections. The peak in the conductance of the FIS contact at the zero potential for the (110)-oriented superconductor disappears rapidly as the polarization of a ferromagnet increases, whereas for the (100)-oriented superconductor it appears. The physical reason for this behavior of conductance is discussed.Comment: 8 pages, 4 figure

Boundary resistance in magnetic multilayers

Quasiclassical boundary conditions for electrochemical potentials at the interface between diffusive ferromagnetic and non-magnetic metals are derived for the first time. An expression for the boundary resistance accurately accounts for the momentum conservation law as well as essential gradients of the chemical potentials. Conditions are established at which spin-asymmetry of the boundary resistance has positive or negative sign. Dependence of the spin asymmetry and the absolute value of the boundary resistance on the exchange splitting of the conduction band opens up new possibility to estimate spin polarization of the conduction band of ferromagnetic metals. Consistency of the theory is checked on existing experimental data.Comment: 8 pages, 3 figures, designed using IOPART styl

Formation of Multicharged Ions at Quasi-Gasdynamic Plasma Confinement in a Mirror trap

It was shown in [1] that an increase in plasma density Ne in sources of multicharged ions leads to a substantial increase of ion current and improves slightly the ion distribution over charge states. Validity of this statement was verified in experiments with plasma densities not exceeding several units of 1012 cm-3. It was revealed [2] that, for the electron densities exceeding 1013 cm-3, the regime of plasma confinement in a trap changes significantly, the scaling described in [1] is no longer valid, and the quasi-gasdynamic regime of plasma confinement is realized. The plasma confinement time ti in this regime weakly depends on electron density. Consequently, the parameter governing formation of multicharged ions, Neti , grows as the electron density is increased. This means that an increase in plasma density results not only in an increase in the total ion current but also in the shift of the ion charge state distribution towards higher charge states. The present work concerns experimental investigation of the quasi-gasdynamic regime of confinement of a hot plasma in a direct magnetic trap and formation of multicharged ions in this regime. Experiments were conducted on the setup described in detail in [3]. Millimeter wave radiation with maximum power W=130 kW, frequency f=37.5 GHz, and pulse duration up to 1.5 ms was focused along magnetic field lines into a simple mirror trap with mirror ratio 3.4, length 25 cm, and maximum magnetic field 2.5 T. The temperature and density of the electrons were determined from spectral analysis of X-ray bremsstrahlung of plasma in the 2-20 keV range and from the transmission factor of diag-nostic microwave radiation through the plasma. It is concluded that a quasi-gasdynamic regime of plasma confinement is realized. Ion distribution over charge states in the quasi-gasdynamic regime is calculated and the re-sults obtained are compared with experimental data. A strong effect of anisotropy of the electron distribution function over energies on the efficiency of plasma confinement and formation of multicharged ions is considered. Problems of plasma stability in an axisymmetric mirror trap un-der powerful microwave pumping are addressed

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

Design and Status of the Dipole Spectrometer Magnet for the ALICE Experiment

Proposal of abstract for MT16, Tallahesse, Florida, 26th September to 2nd October 1999.A large Dipole Magnet is required for the Muon Arm Spectrometer of the ALICE experiment at the LHC.The absence of strong requirements on the symmetry and homogeneity of the magnetic field has lead to a design dominated by economic and feasibility considerations.In March 1997 the decision was taken to build a resistive dipole magnet for the muon spectrometer of the ALICE experiment. Since then, design work has been pursued in JINR/Russia and at CERN. While a common concept has been adopted for the construction of the steel core, two different proposals have been made for the manufacturing technology of the excitation coils. In both cases, however, the conductor material will be Aluminium.The general concept of the dipole magnet is based on a window frame return yoke, fabricated from low carbon steel sheets. The flat vertical poles follow the defined acceptance angle of 9 degrees. The excitation coils are of saddle type. The coils are wound from large hollow Aluminium profiles. They are cooled by pressurized demineralised water. The coil ends are located to both sides of the magnet yoke and determine the overall length of the magnet. The main flux direction in the gap is horizontal and perpendicular to the LHC beam axis.Both coil concepts and the underlying manufacturing technology are compared and the present status of the development of the magnet is described

The influence of spin-dependent phases of tunneling electrons on the conductance of a point ferromagnet/isolator/superconductor contact

The Andreev reflection probability for a ferromagnet/isolator/superconductor (FIS) contact at the arbitrary spin-dependent amplitudes of the electron waves transmitted through and reflected from the potential barrier is found. It is shown that Andreev reflection probabilities of electron and hole excitations in the FIS contact are different. The energy levels of Andreev bound states are found. The ballistic conductance of the point FIS contact is calculated.Comment: e.g.:10 pages, 3 figures added in tex. file: abstract and article's titl