Superconducting triplet spin valve

We study the critical temperature Tc of SFF trilayers (S is a singlet superconductor, F is a ferromagnetic metal), where the long-range triplet superconducting component is generated at noncollinear magnetizations of the F layers. We demonstrate that Tc can be a nonmonotonic function of the angle α between the magnetizations of the two F layers. The minimum is achieved at an intermediate α, lying between the parallel (P, α = 0) and antiparallel (AP, α = π) cases. This implies a possibility of a "triplet" spin-valve effect: at temperatures above the minimum Tc Tr but below Tc P and Tc AP, the system is superconducting only in the vicinity of the collinear orientations. At certain parameters, we predict a reentrant Tc(α) behavior. At the same time, considering only the P and AP orientations, we find that both the "standard" (Tc P Tc AP) switching effects are possible depending on parameters of the system. © 2010 Pleiades Publishing, Ltd

Josephson tunnel junctions with strong ferromagnetic interlayer

The dependence of the critical current density j_c on the ferromagnetic interlayer thickness d_F was determined for Nb/Al_2O_3/Cu/Ni/Nb Josephson tunnel junctions with ferromagnetic \Ni interlayer from very thin film thicknesses (\sim 1 nm) upwards and classified into F-layer thickness regimes showing a dead magnetic layer, exchange, exchange + anisotropy and total suppression of j_c. The Josephson coupling changes from 0 to pi as function of d_F, and -very close to the crossover thickness- as function of temperature. The strong suppression of the supercurrent in comparison to non-magnetic \Nb/Al_2O_3/Cu/Nb junctions indicated that the insertion of a F-layer leads to additional interface scattering. The transport inside the dead magnetic layer was in dirty limit. For the magnetically active regime fitting with both the clean and the dirty limit theory were carried out, indicating dirty limit condition, too. The results were discussed in the framework of literatureComment: 8 pages, 5 pictures v2: major conceptual change

Superconducting triplet spin valve

We study the critical temperature Tc of SFF trilayers (S is a singlet superconductor, F is a ferromagnetic metal), where the long-range triplet superconducting component is generated at noncollinear magnetizations of the F layers. We demonstrate that Tc can be a nonmonotonic function of the angle α between the magnetizations of the two F layers. The minimum is achieved at an intermediate α, lying between the parallel (P, α = 0) and antiparallel (AP, α = π) cases. This implies a possibility of a "triplet" spin-valve effect: at temperatures above the minimum Tc Tr but below Tc P and Tc AP, the system is superconducting only in the vicinity of the collinear orientations. At certain parameters, we predict a reentrant Tc(α) behavior. At the same time, considering only the P and AP orientations, we find that both the "standard" (Tc P Tc AP) switching effects are possible depending on parameters of the system. © 2010 Pleiades Publishing, Ltd

Proximity effects in superconducting triplet spin-valve F2/F1/S

©2014 Elsevier B.V. All rights reserved. We investigate the critical temperature Tc of F2/F1/S trilayers (Fi is a ferromagnetic metal and S is a singlet superconductor), where the long-range triplet superconducting component is generated at noncollinear magnetizations of the F layers. In this paper we demonstrate a possibility of the spin-valve effect mode selection (standard switching effect, the triplet spin-valve effect or reentrant Tc(α) dependence) by the variation of the F2/F1 interface transparency

Role of interface transparency and exchange field in the superconducting triplet spin-valve effect

© (2015) Trans Tech Publications, Switzerland. We study the superconducting transition temperature Tc of F2/F1/S trilayers (Fi is a metallic ferromagnet, S is a s-superconductor), where the long-range triplet superconducting component is generated at canted magnetizations of the F layers. In this paper we show that it is possible to realize different spin-valve effect modes - the standard switching effect, the triplet spin-valve effect, reentrant Tc(α) dependence or reentrant Tc(α) dependence with the inverse switching effect - by variation of the F2/F1 interface transparency or the exchange splitting energy. In addition, we show that position of the Tc minimum can be changed by joint variation of the F2/F1 interface transparency and the layer thicknesses

Frequency and size dependence of ac Josephson effect in Nb/Au/YBCO heterojunctions

Abstract. High frequency dynamics of Nb/Au/YBaCuO heterojunctions on tilted NdGaO 3 substrates have been studied. The both integer and non-integer Shapiro steps have been observed at mm-wave frequencies. Unconventional dependence of the critical current and the amplitudes of Shapiro steps vs. applied microwave power have been registered. Observed behavior deviates from existing theories of Josephson effect for junctions made from conventional or d-wave superconductors. Although the maximal size of the heterojunctions was smaller than the Josephson penetration depth, calculated from an averaged value of the critical current density, the experimental magnetic field dependences I C (H) deviate from the Fraunhofer pattern, pointing on non-uniform distribution of superconducting current density. Experimental results could be speculatively explained by origination of self-induced fractional magnetic vortices, which may take place in a junction where the amplitude and the phase of superconducting current alternate significantly over the junction area. Introducing a new lengthscale, which is much smaller than the Josephson penetration depth, the fractional vortices are considered, modifying the high frequency dynamics, namely the ac Josephson effect. Experimental results have been analyzed taking into account the second harmonic of superconducting current-phase relation and the influence of heterojunction capacitance. Introduction It is known that in metal-oxide superconductors with high critical temperature, for example in YBCO, the d-wave symmetry of superconducting order parameter (D-superconductor) is predominant one in the basal (a-b) plan

Spin-polarized supercurrents for spintronics: a review of current progress

During the past 15 years a new field has emerged, which combines superconductivity and spintronics, with the goal to pave a way for new types of devices for applications combining the virtues of both by offering the possibility of long-range spin-polarized supercurrents. Such supercurrents constitute a fruitful basis for the study of fundamental physics as they combine macroscopic quantum coherence with microscopic exchange interactions, spin selectivity, and spin transport. This report follows recent developments in the controlled creation of long-range equal-spin triplet supercurrents in ferromagnets and its contribution to spintronics. The mutual proximity-induced modification of order in superconductor-ferromagnet hybrid structures introduces in a natural way such evasive phenomena as triplet superconductivity, odd-frequency pairing, Fulde-Ferrell-Larkin-Ovchinnikov pairing, long-range equal-spin supercurrents, $\pi$-Josephson junctions, as well as long-range magnetic proximity effects. All these effects were rather exotic before 2000, when improvements in nanofabrication and materials control allowed for a new quality of hybrid structures. Guided by pioneering theoretical studies, experimental progress evolved rapidly, and since 2010 triplet supercurrents are routinely produced and observed. We have entered a new stage of studying new phases of matter previously out of our reach, and of merging the hitherto disparate fields of superconductivity and spintronics to a new research direction: super-spintronics.Comment: 95 pages, 23 Figures; published version with minor typos corrected and few references adde

Conductance spectroscopy in ferromagnet-superconductor hybrids

We present a theoretical model for the proximity effect in F–SFF–F structures (where F is a ferromagnet and S is a superconductor) with non-collinear magnetization vectors in the F-layers and with arbitrary magnitudes of exchange fields. The electrical conductance of these structures is analyzed within the Keldysh–Usadel formalism in the diffusive regime as a function of the misorientation angle between magnetizations of the F-layers and transparencies of the SF and FF interfaces. We show that long-range triplet superconducting correlations manifest themselves either as a zero-bias peak in the case of perfect transparency of the FF interface, or as a two-peak structure in the case of finite transparency. The predicted features may serve as a diagnostic tool for the characterization of interfaces in superconducting hybrid structures

Distribution of pairing functions in superconducting spin-valve switching modes

We investigated the critical temperature Tc of SF1F2 trilayers (S is a singlet superconductor, F1 and F2 are ferromagnetic metals), where the long-range triplet superconducting pairing is generated at canted magnetizations of the F layers. We examined the spin-singlet and spin-triplet pairing distributions and their amplitudes as a function of the layers thicknesses under different values of the angle a in the SF1F2 structure to clarify which one of the pairing distributions and how may affect the superconducting Tc