[{"type":"speech","title":"Crossover from 2D-3D behaviour in superconducting Nb\/CuNi bilayers in a magnetic field","issued":{"date-parts":[["2009"]]},"author":[{"family":"Kehrle","given":"J. M."},{"family":"Zdravkov","given":"V."},{"family":"Obermeier","given":"G."},{"family":"Morari","given":"R."},{"family":"Antropov","given":"E."},{"family":"Prepelitsa","given":"A."},{"family":"M\u00fcller","given":"C."},{"family":"Wixforth","given":"A."},{"family":"Horn","given":"S."},{"family":"Tidecks","given":"R."},{"family":"Sidorenko","given":"A."}],"note":"Fr\u00fchjahrstagung DPG, Fachverband Tiefe Temperaturen, Dresden, 22.-27.M\u00e4rz 2009 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.44(2009) TT 32.16","abstract":"Low Temperature Physics Division (TT)\nWednesday\n51 01 19, 01314 Dresden, Germany \u2014 2 International Center for Condensed Matter Physics, 70904-910, Bras\u00b4\n\u0131lia-DF, Brazil \u2014 3 Faculty of\nMathematics and Physics, Charles University, Ke Karlovu 3, 12116\nPrague 2, Czech Republic \u2014 4 Institute of Physics, Academy of Sciences, Cukrovarnick\u00b4 10, 16253 Prague 6, Czech Republic \u2014 5 Max\nPlanck Institute for Metals Research, D-70506 Stuttgart, Germany\nA superconducting layer exposed to a perpendicular electric and parallel magnetic \ufb01eld is considered within the Ginzburg-Landau (GL)\napproach. The GL equation is solved near the surface and the surface energy is calculated [1,2]. The nucleation critical \ufb01eld is shown to\nbe changed in dependence on the magnetic and electric \ufb01eld. Special\nconsideration is payed to the induced magnetic-\ufb01eld e\ufb00ect caused by\ndiamagnetic surface currents. The latter e\ufb00ect constitutes the main\ncontribution to the e\ufb00ective inverse capacitance which determines the\ne\ufb00ective penetration depth. The surface energy becomes strongly dependent on the width of the sample. An experimental realization is\nsuggested for determining the change in the e\ufb00ective capacitance of\nthe layer.\n[1] Phys. Rev. B 78 (2008)054525\n[2] arXiv 0804.0138\nTT 32.13\nWed 14:00\nP1A\n\u00b4\nThe lateral S-(S\/F)-S Josephson junctions \u2014 \u2022Ondrej Vavra,\nWolfgang Pfaff, and Christoph Strunk \u2014 Inst. for Exp. and\nUp to now the proximity e\ufb00ect at the superconductor-ferromagnet\n(S-F) interface was mainly demonstrated by the transport properties\nacross the S-F interface [A.A. Golubov, M.Yu. Kupriyanov, and E.\nIlichev, Rev. Mod. Phys. 76, 411 (2004).]. We present the results\non lateral transport along the S-F interface and its utilization as a\nJosephson junction. We have prepared Nb based Josephson junctions\nwhich consist of Nb micro bridges with a Pd0.95 Fe0.05 or Fe strip deposited perpendicular to the bridge. The width of the ferromagnetic\nstrip was varied between 50 and 800 nm. The critical current (IC ) of\nthe Nb-Pd0.95 Fe0.05 and Nb-Fe bi-layer, respectively, is found to be\nsigni\ufb01cantly reduced by the proximity e\ufb00ect with the ferromagnet.\nWe have studied the temperature and magnetic \ufb01eld (B) dependencies of the critical current. In magnetic \ufb01eld an interference pattern\nIC (B) is observed. In perpendicular magnetic \ufb01eld the junction exhibits IC (B) dependence similar to a Fraunhofer pattern which proves\nthe dc Josephson e\ufb00ect. We also investigate the dependence of IC (B)\noscillations on the orientation of the magnetic \ufb01eld. The control of\nthe Josephson junction parameters is provided by third electrode connected to the F strip.\nTT 32.14\nWed 14:00\nP1A\nObservation of absolute negative resistance in mesoscopic\nsamples of a-NbGe \u2014 \u2022Florian Otto1 , Ante Bilu\u02c7ic1,2 , Dinko\ns\u00b4\n\u00b4\n\u00a8\nBabic3 , Christoph Surgers4 , and Christoph Strunk1 \u2014 1 Inst. for\nExp. and Appl. Physics, Univ. Regensburg, Germany \u2014 2 Fac. of Nat.\nSciences, Univ. of Split, Croatia \u2014 3 Dept. Physics, Univ. Zagreb,\nCroatia \u2014 4 Phys. Inst. and DFG CFN, Univ. Karlsruhe, Germany\nLocal and nonlocal measurements on mesoscopic samples of amorphous\nNbGe, a high-\u03ba type-II superconductor with very low pinning, reveal\npeculiar features in close vicinity of the transition temperature Tc : in\nabsence of magnetic \ufb01eld, both local and nonlocal DC voltage current\ncharacteristics clearly display absolute negative resistance in a small\ninterval around zero current and a small temperature range immediately below Tc . At the same time, a negative voltage is also observed\nin both local and nonlocal measurements of R(T ). The temperatures\nat which this occurs are consistently found to be around 0.95-0.96 Tc ,\nwhich is clearly below the narrow superconducting transition region.\nUpon application of small external magnetic \ufb01elds on the order of\nB = 50 mT, the e\ufb00ect can be suppressed. The origin of these completely unexpected features is not clear.\nTT 32.15\nWed 14:00\nP1A\nSpin mixing at Superconductor Ferromagnet Interfaces\n\u00a8\nprobed by non-local transport \u2014 \u2022Florian Hubler1,2 , Detlef\n\u00a8\nGermany\nWe present experimental results on non-local conductance in multiter-\nminal hybrid structures, where two or more ferromagnetic (F) contacts\nare attached to a single superconductor (S). For contacts with an insulating (I) tunnel barrier, and at energies below the energy gap of\nthe superconductor, the non-local conductance is determined by the\ncompetition of crossed Andreev re\ufb02ection (CAR) and elastic cotunneling (EC). In FISIF structures, the contributions of CAR and EC are\nexpected to depend on the orientation of the magnetisation of the F\ncontacts. Recently, an asymmetric conductance signal as consequenc\nof a \ufb01nite spin-mixing angle has been predicted [1]. We observe \ufb01rst\nsigns for similar signals in our structures.\n[1] Kalenkov and Zaikin, Phys. Rev. B 76, 224506 (2007)\nTT 32.16\nWed 14:00\nP1A\nNb\/CuNi bilayers in a magnetic \ufb01eld \u2014 \u2022Jan-Michael\n\u00a8\n\u00a8\nTidecks2 , and Anatolie Sidorenko1,2,3 \u2014 1 Institute of Electronic\nEngineering and Industrial Technologies ASM, Kishinev, MD2028,\nMoldova \u2014 2 Institut f\u00a8r Physik, Universit\u00a8t Augsburg, D-86159 Augsu\nA dimensional crossover in an external magnetic \ufb01eld, applied parallel\nto the layers, has been found for superconductor\/ferromagnet (S\/F)\nbilayers of Nb\/CuNi. For decreasing temperature the square-root 2Dbehaviour of the upper critical magnetic \ufb01eld, Bc2||(T) on the temperature, in the vicinity of the critical temperature Tc switches to the\nlinear 3D-behaviour below the crossover temperature, Tcr. The 2D-3D\ncrossover also occurs concerning the temperature dependence of superconducting \ufb02uctuations in the critical \ufb02uctuation regime. The \ufb02uctuation conductivity exhibits a 2D-behaviour in zero- and weak magnetic\n\ufb01elds close to Tc, switching to a 3D-behaviour in strong magnetic\n\ufb01elds at low temperatures. In a S\/F bilayer the quasi-one dimensional\nFulde-Ferrel-Larkin-Ovchinnikov (FFLO) like state is realized, so that\nthe superconducting properties are governed by interference e\ufb00ects of\nthe pairing wave functions, i.e. by the pairing function \ufb02ux through\nthe S\/F interface.\nTT 32.17\nWed 14:00\nP1A\nStructure and local electronic properties of Ag and Co\/Ag\n\u00a8\non Nb(110) \u2014 \u2022Tihomir Tomanic1 , Christoph Surgers1 , and\n\u00a8\nThe local variation of the superconductive order parameter in hybrid\nstructures of a superconductor S with a normal metal N or ferromagnet F is a topic of current interest. We have started a study of Ag\nand Co islands on Nb via scanning tunneling microscopy (STM) and\nspectroscopy (STS) at low temperatures.\nAs a prerequisite, we report on the surface structure of clean Nb(110)\nsingle crystals obtained after Ar+ sputtering and \ufb02ash heating up to\n2300 \u25e6 C in ultra-high vacuum. The atomic structure as well as the\nlocal superconducting properties have been explored by STM and STS\nat T = 2.5 and T = 4.2 K. We have studied the topography of a thin\nAg overlayer (nominal thickness 5nm) on Nb(110) and of Co islands\non top of the Ag overlayer. First results of the local electronic density of states derived from the current-voltage characteristics will be\nTT 32.18\nWed 14:00\nP1A\nAngle-dependent investigation of the up","kit-publication-id":"220075164"}]