2,589 research outputs found
Ferromagnet-superconductor proximity effect: The clean limit
We study theoretically the influence of ferromagnetic metals on a
superconducting film in the clean limit. Using a self-consistent solution of
the Bogoliubov--de Gennes equation for a ferromagnet-superconductor-ferromagnet
double junction we calculate the pair potential and conductance spectra as a
function of the superconducting layer thickness for different strengths of
ferromagnets and interface transparencies. We find that the pair potential and
the critical temperature are weakly perturbed by the exchange interaction and
do not drop to zero for any finite . On the other hand, for thin
superconducting films charge transport is spin polarized and exhibits a
significant dependence on the ferromagnetic strength and magnetization
alignment.Comment: 5 pages, 4 figure
Spin-polarized currents in superconducting films
We present a microscopic theory of coherent quantum transport through a
superconducting film between two ferromagnetic electrodes. The scattering
problem is solved for the general case of
ferromagnet/superconductor/ferromagnet (FSF) double-barrier junction, including
the interface transparency from metallic to tunnel limit, and the Fermi
velocity mismatch. Charge and spin conductance spectra of FSF junctions are
calculated for parallel (P) and antiparallel (AP) alignment of the electrode
magnetization. Limiting cases of nonmagnetic normal-metal electrodes (NSN) and
of incoherent transport are also presented. We focus on two characteristic
features of finite size and coherency: subgap tunneling of electrons, and
oscillations of the differential conductance. Periodic vanishing of the Andreev
reflection at the energies of geometrical resonances above the superconducting
gap is a striking consequence of the quasiparticle interference. Also, the
non-trivial spin-polarization of the current is found for FSF junctions in AP
alignment. This is in contrast with the incoherent transport, where the
unpolarized current is accompanied by excess spin accumulation and destruction
of superconductivity. Application to spectroscopic measurements of the
superconducting gap and the Fermi velocity is also discussed.Comment: 11 pages, 11 figure
Quasiparticle Spectrum of Vortices in Cuprates
The quasiparticle excitation spectrum of an isolated vortex in a clean
layered d-wave superconductor is calculated, using both the Bogoliubov--de
Gennes and the quasiclassical Eilenberger equations. Analytical solutions are
obtained within the model of step-variation of the gap function, adjusting the
Caroli, de Gennes and Matricon approach for low-lying excitations in cuprates.
A large peak in the density of states in the "pancake" vortex core is found,
caused by the two-dimensional and strong coupling nature of high-temperature
superconductivity.Comment: 8 pages, Latex, uses spie1.sty, 6 eps figures, published in SPIE
Proceedings, Vol. 3481 (SPIE, Bellingham, 1998), p. 106-11
Coherent effects in double-barrier ferromagnet/superconductor/ferromagnet junctions
Coherent quantum transport in ferromagnet/superconductor/ferromagnet (FSF)
double-barrier junctions is studied. Analytic expressions for charge and spin
conductance spectra are derived for the general case of insulating interfaces
(from metallic to tunnel limit), the Fermi velocity mismatch, and for parallel
(P) and antiparallel (AP) alignment of the electrode magnetizations. We focus
on two characteristic features of finite size and coherency: subgap electronic
transport, and oscillations of the differential conductance. Periodic vanishing
of the Andreev reflection at the energies of geometrical resonances above the
superconducting gap is a striking consequence of the quasiparticle
interference. In contrast with the case of incoherent transport, a non-trivial
spin-polarization without the excess spin accumulation is found for the AP
alignment.Comment: 12 pages, 5 figure
Tutte and Jones polynomials of link families
This article contains general formulas for Tutte and Jones polynomials for
families of knots and links given in Conway notation and "portraits of
families"-- plots of zeroes of their corresponding Jones polynomials
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