Superconducting crossed correlations in ferromagnets: implications for thermodynamics and quantum transport

It is demonstrated that non local Cooper pairs can propagate in ferromagnetic electrodes having an opposite spin orientation. In the presence of such crossed correlations, the superconducting gap is found to depend explicitly on the relative orientation of the ferromagnetic electrodes. Non local Cooper pairs can in principle be probed with dc-transport. With two ferromagnetic electrodes, we propose a ``quantum switch'' that can be used to detect correlated pairs of electrons. With three or more ferromagnetic electrodes, the Cooper pair-like state is a linear superposition of Cooper pairs which could be detected in dc-transport. The effect also induces an enhancement of the ferromagnetic proximity effect on the basis of crossed superconducting correlations propagating along domain walls.Comment: 4 pages, RevTe

Critical temperature of superconductor/ferromagnet bilayers

Superconductor/ferromagnet bilayers are known to exhibit nontrivial dependence of the critical temperature T_c on the thickness d_f of the ferromagnetic layer. We develop a general method for investigation of T_c as a function of the bilayer's parameters. It is shown that interference of quasiparticles makes T_c(d_f) a nonmonotonic function. The results are in good agreement with experiment. Our method also applies to multilayered structures.Comment: 4 pages, 2 EPS figures; the style file jetpl.cls is included. Version 2: typos correcte

Composite excitation of Josephson phase and spin waves in Josephson junctions with ferromagnetic insulator

Coupling of Josephson-phase and spin-waves is theoretically studied in a superconductor/ferromagnetic insulator/superconductor (S/FI/S) junction. Electromagnetic (EM) field inside the junction and the Josephson current coupled with spin-waves in FI are calculated by combining Maxwell and Landau-Lifshitz-Gilbert equations. In the S/FI/S junction, it is found that the current-voltage (I-V) characteristic shows two resonant peaks. Voltages at the resonant peaks are obtained as a function of the normal modes of EM field, which indicates a composite excitation of the EM field and spin-waves in the S/FI/S junction. We also examine another type of junction, in which a nonmagnetic insulator (I) is located at one of interfaces between S and FI. In such a S/I/FI/S junction, three resonant peaks appear in the I-V curve, since the Josephson-phase couples to the EM field in the I layer.Comment: 16 pages, 5 figure

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

Layered ferromagnet-superconductor structures: the π\pi state and proximity effects

We investigate clean mutilayered structures of the SFS and SFSFS type, (where the S layer is intrinsically superconducting and the F layer is ferromagnetic) through numerical solution of the self-consistent Bogoliubov-de Gennes equations for these systems. We obtain results for the pair amplitude, the local density of states, and the local magnetic moment. We find that as a function of the thickness $d_F$ of the magnetic layers separating adjacent superconductors, the ground state energy varies periodically between two stable states. The first state is an ordinary "0-state", in which the order parameter has a phase difference of zero between consecutive S layers, and the second is a "$\pi$-state", where the sign alternates, corresponding to a phase difference of $\pi$ between adjacent S layers. This behavior can be understood from simple arguments. The density of states and the local magnetic moment reflect also this periodicity.Comment: 12 pages, 10 Figure

First identification of Bartonella coopersplainsensis in wild rodents (Rattus norvegicus) in Greece

Η μελέτη αυτή ήταν μια πρώτη προσπάθεια για ανίχνευση της Bartonella sp. σε ιστούς (ήπαρ και καρδιά) πουπάρθηκαν από άγρια τρωκτικά {Rattus norvegicus) στην κεντρική Ελλάδα. Εξετάστηκαν δεκαοκτώ (18) δείγματα ήπατος και δεκαοκτώ (18) δείγματα καρδιάς, τα οποία προέρχονταν από είκοσι τρία (23) ζώα. Δυο (2) δείγματα ήπατος βρέθηκαν θετικάενώ όλα τα δείγματα καρδιάς ήταν αρνητικά για το γονίδιο 16S-23S intergenic spacer rDNA της Bartonella sp. Η αλληλουχίατων βάσεων του DNA των θετικών δειγμάτων και η σύγκριση με τα διαθέσιμα δεδομένα της GenBank με τη χρησιμοποίησητου προγράμματος BLAST, αποκάλυψε το ίδιο είδος Bartonella και στα δύο θετικά δείγματα με 100% ομοιότητα με τηναλληλουχία των βάσεων της Bartonella coopersplainsensis. This study was a preliminary attempt to detect Bartonella sp. in tissues (liver and heart) obtained from wild rodents {Rattus norvegicus) in central Greece. Eighteen (18) liver and eighteen (18) heart samples were examined, which were obtained from twenty three (23) animals. Two (2) liver samples were found positive, while the heart samples examined were found negative for Bartonella sp. 16S-23S intergenic spacer rDNA gene by PCR. Sequencing of the positive PCR products and comparison with those available in GenBank using the BLAST program revealed the same species of Bartonella in both positive samples with 100% sequence homology to Bartonella coopersplainsensis

Crossed Andreev reflection at ferromagnetic domain walls

We investigate several factors controlling the physics of hybrid structures involving ferromagnetic domain walls (DWs) and superconducting (S) metals. We discuss the role of non collinear magnetizations in S/DW junctions in a spin $\otimes$ Nambu $\otimes$ Keldysh formalism. We discuss transport in S/DW/N and S/DW/S junctions in the presence of inelastic scattering in the domain wall. In this case transport properties are similar for the S/DW/S and S/DW/N junctions and are controlled by sequential tunneling of spatially separated Cooper pairs across the domain wall. In the absence of inelastic scattering we find that a Josephson current circulates only if the size of the ferromagnetic region is smaller than the elastic mean free path meaning that the Josephson effect associated to crossed Andreev reflection cannot be observed under usual experimental conditions. Nevertheless a finite dc current can circulate across the S/DW/S junction due to crossed Andreev reflection associated to sequential tunneling.Comment: 18 pages, 8 figures, references added at the end of the introductio