Manifestation of New Interference Effects in Superconductor/Ferromagnet Spin Valve

Superconductor/ferromagnet (S/F) spin valve effect theories based on the S/F proximity phenomenon assume that the superconducting transition temperature Tc of F1/F2/S or F1/S/F2 trilayers for parallel magnetizations of the F1- and F2-layers (TcP) are smaller than for the antiparallel orientations (TcAP). Here, we report for CoOx/Fe1/Cu/Fe2/In multilayered systems with varying Fe2-layer thickness the sign-changing oscillating behavior of the spin valve effect \Delta Tc=TcAP-TcP. Our measurements revealed the full direct spin valve effect with TcAP>TcP for Fe2-layer thickness dFe2<1 nm and the full inverse (TcAP=1 nm. Interference of Cooper pair wave functions reflected from both surfaces of the Fe2-layer appear as the most probable reason for the observed behavior of \Delta Tc.Comment: Accepted for publication in PR

Full spin switch effect for the superconducting current in a superconductor/ferromagnet thin film heterostructure

Superconductor/ferromagnet (S/F) proximity effect theory predicts that the superconducting critical temperature of the F1/F2/S or F1/S/F2 trilayers for the parallel orientation of the F1 and F2 magnetizations is smaller than for the antiparallel one. This suggests a possibility of a controlled switching between the superconducting and normal states in the S layer. Here, using the spin switch design F1/F2/S theoretically proposed by Oh et al. [Appl. Phys. Lett. 71, 2376 (1997)], that comprises a ferromagnetic bilayer separated by a non-magnetic metallic spacer layer as a ferromagnetic component, and an ordinary superconductor as the second interface component, we have successfully realized a full spin switch effect for the superconducting current.Comment: 5 pages, 4 figure

Evidence for Triplet Superconductivity in a Superconductor-Ferromagnet Spin Valve

We have studied the dependence of the superconducting (SC) transition temperature on the mutual orientation of magnetizations of Fe1 and Fe2 layers in the spin valve system CoO_x/Fe1/Cu/Fe2/Pb. We find that this dependence is nonmonotonic when passing from the parallel to the antiparallel case and reveals a distinct minimum near the orthogonal configuration. The analysis of the data in the framework of the SC triplet spin valve theory gives direct evidence for the long-range triplet superconductivity arising due to noncollinearity of the two magnetizations.Comment: 5 pages (including 4 EPS figures). Version 2: final version as published in PR

Manifestation of New Interference Effects in Superconductor/Ferromagnet Spin Valve

Superconductor/ferromagnet (S/F) spin valve effect theories based on the S/F proximity phenomenon assume that the superconducting transition temperature Tc of F1/F2/S or F1/S/F2 trilayers for parallel magnetizations of the F1- and F2-layers (TcP) are smaller than for the antiparallel orientations (TcAP). Here, we report for CoOx/Fe1/Cu/Fe2/In multilayered systems with varying Fe2-layer thickness the sign-changing oscillating behavior of the spin valve effect \Delta Tc=TcAP-TcP. Our measurements revealed the full direct spin valve effect with TcAP>TcP for Fe2-layer thickness dFe2<1 nm and the full inverse (TcAP<TcAP) spin valve effect for dFe2>=1 nm. Interference of Cooper pair wave functions reflected from both surfaces of the Fe2-layer appear as the most probable reason for the observed behavior of \Delta Tc.Comment: Accepted for publication in PR

Observation of the "Inverse" spin valve effect in a Ni/V/Ni trilayer system

An experimental study of magnetic and superconducting properties of a trilayer Ni/V/Ni thin film system grown on single-crystalline MgO(001) substrate is reported. The field dependence of the superconducting transition temperature T c for samples comprising Ni layers with similar values of the coercive field H c reveals no anomalies. However, in samples with different thicknesses of the nickel layers the difference in H c amounts up to ΔH c ~ 1.8 kOe, thus enabling to manipulate the relative orientations of the layers' magnetization by an external magnetic field. Surprisingly, for these samples the T c for the parallel orientation of the magnetizations of the Ni layers is higher, in a certain magnetic field range, than for the antiparallel one, at odds with theoretical predictions. Possible reasons of this contradiction are discussed. © Pleiades Publishing, Ltd., 2009

Strongly localized polaritons in an array of trapped two-level atoms interacting with a light field

We propose a new type of spatially periodic structure, i.e. polaritonic crystal (PolC), to observe a "slow"/"stopped" light phenomenon due to coupled atom-field states (polaritons) in a lattice. Under the tightbinding approximation, such a system realizes an array of weakly coupled trapped two-component atomic ensembles interacting with optical field in a tunnel-coupled one dimensional cavity array. We have shown that the phase transition to the superfluid Bardeen-Cooper-Schrieffer state, a so-called (BCS)-type state of low branch polaritons, occurs under the strong coupling condition. Such a transition results in the appearance of a macroscopic polarization of the atomic medium at non-zero frequency. The principal result is that the group velocity of polaritons depends essentially on the order parameter of the system, i.e. on the average photon number in the cavity array.Comment: 16 pages, 6 figure