Spin-polarized neutron reflectivity: A probe of vortices in thin-film superconductors

URL:http://link.aps.org/doi/10.1103/PhysRevB.59.14692 DOI:10.1103/PhysRevB.59.14692It is demonstrated that the specular reflectivity of spin-polarized neutrons can be used to study vortices in a thin-film superconductor. Experiments were performed on a 6000 Å thick c-axis film of YBa2Cu3O7-x with the magnetic field applied parallel to the surface. A magnetic hysteresis loop was observed for the spin-polarized reflection and, from these data, the average density of vortices was extracted. A model is presented which relates the specular reflectivity to the one-dimensional spatial distribution of vortices in the direction perpendicular to the surface. Unlike other techniques, neutron reflectivity observes vortices in a geometry where they are parallel to the interface.Support ~P.F.M., S.W.H.! from the Midwest Superconductivity Consortium ~MISCON! under the U.S. DOE Grant No. DE-FG02-90ER45427, the NSF DMR Grant No. 96-23827, and ~L.H.G., E.P.! from the NSF DMR Grant No. 94-21957, and ONR Grant No. N-00014-95-1-0831 is gratefully acknowledged. We thank E. Fullerton for useful discussions and D.H. Lowndes for help in understanding the surface roughness of oxide superconductors

Observation of the superconducting proximity effect in Nb/InAs and NbNx/InAs by Raman scattering

URL:http://link.aps.org/doi/10.1103/PhysRevB.66.134530 DOI:10.1103/PhysRevB.66.134530High-quality thin Nb and NbN films (60-100 Å) are grown on (100) n+-InAs (n=1019cm-3) substrates by dc-magnetron sputter deposition. Studies of the electronic properties of interfaces between the superconductor and the semiconductor are done by Raman scattering measurements. The superconducting proximity effect at superconductor-semiconductor interfaces is observed through its impact on inelastic light scattering intensities originating from the near-interface region of InAs. The InAs longitudinal optical phonon LO mode (237cm-1) and the plasmon-phonon coupled modes L- (221cm-1) and L+ (1100 to 1350cm-1), for n+=1×1019-2×1019cm-3 are measured. The intensity ratio of the LO mode (associated with the near-surface charge accumulation region, in InAs) to that of the L- mode (associated with bulk InAs), is observed to increase by up to 40% below the superconducting transition temperature. This temperature-dependent change in light scattering properties is only observed with high quality superconducting films and when the superconductor and the semiconductor are in good electrical contact. A few possible mechanisms of the observed effect are proposed.We gratefully acknowledge support from the United States Department of Energy through Materials Research Laboratory~Grant No. DEFG02-96ER45439! ~I.V.R., A.C.A., L.H.G., T.A.T., J.F.D., P.W.B., J.F.K.!, and from the United States Department of Energy through Midwest Superconductivity Consortium ~MISCON! ~Grant No. DE FG02-90ER45427! and the NSF ~Grant No. DMR 96-23827! ~S.W.H., P.F.M.!. SEM, XRD, XPS, and RBS materials characterizations were performed at the Center for Microanalysis of Materials and Microfabrication Center at Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana- Champaign ~Grant No. DE FG02-96ER45439!. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the United States Department of Energy under Contract No. DE-AC04-94AL85000