Multiple Andreev reflections in diffusive SNS structures

We report new measurements on sup-gap energy structure originating from multiple Andreev reflections in mesoscopic SNS junctions. The junctions were fabricated in a planar geometry with high transparency superconducting contacts of Al deposited on highly diffusive and surface d-doped n++-GaAs. For samples with a normal GaAs region of active length 0.3um the Josephson effect with a maximal supercurrent Ic=3mA at T=237mK was observed. The sub-gap structure was observed as a series of local minima in the differential resistance at dc bias voltages V=2D/ne with n=1,2,4 i.e. only the even sub-gap positions. While at V=2D/e (n=1) only one dip is observed, the n=2, and the n=4 sub-gap structures each consists of two separate dips in the differential resistance. The mutual spacing of these two dips is independent of temperature, and the mutual spacing of the n=4 dips is half of the spacing of the n=2 dips. The voltage bias positions of the sub-gap differential resistance minima coincide with the maxima in the oscillation amplitude when a magnetic field is applied in an interferometer configuration, where one of the superconducting electrodes has been replaced by a flux sensitive open loop.Comment: 20 pages, 7 figure

Structural and magnetic properties of (NdBa)MnO3 films on lattice-matched substrates

Structural and magnetic properties of (NdBa)MnO3 thin films grown on several perovskite substrates by pulsed laser deposition are presented. A high crystal quality epitaxial film with smooth surface and low level of internal strain may be grown up to thicknesses of 70 nm. The in-plane distortion of the film lattice by the substrate-introduced compressive strain promotes corresponding changes in the out-of-plane lattice constant, following the volume-preserving dilation. The films under tensile strain are growing totally relaxed. Different oxygenation conditions during depositions induce correlated changes of structural and magnetic properties of the material. The temperature of ferromagnetic transition of the films is around 100 K and increases with expansion of the unit cell. The magnetic moment in saturation is usually higher along the longest lattice constant of the film. An increase of the bi-axial compressive strain introduced by the substrate results in a rapid increase of the magnetic moment of the films. The observed effects may be explained by a high level of local distortions due to difference in the ionic radii of Nd and Ba