[{"type":"speech","title":"Observation of nanostripes and -clusters in NEG superconductors","issued":{"date-parts":[["2009"]]},"author":[{"family":"Koblischka","given":"M. R."},{"family":"Winter","given":"M."},{"family":"Das","given":"P."},{"family":"Koblischka-Veneva","given":"A."},{"family":"Muralidhar","given":"M."},{"family":"Wolf","given":"T."},{"family":"Babu","given":"N. H."},{"family":"Turner","given":"S."},{"family":"van Tendeloo","given":"G."},{"family":"Hartmann","given":"U."}],"note":"Fr\u00fchjahrstagung DPG, Fachverband Tiefe Temperaturen, Dresden, 22.-27.M\u00e4rz 2009 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.44(2009) TT 27.4","abstract":"Low Temperature Physics Division (TT)\nWednesday\nand random matrix theory of chaotic cavities.\nWe further discuss the relevance of intervalley scattering on the magnitude of the weak localization peak.\nTT 26.16\nWed 18:30\nHSZ 03\n\u00a8\nSymmetry Classes in Graphene Quantum Dots \u2014 \u2022Jurgen\n2 Department of Physics, Duke University, Durham, NC 27708, USA\n\u2014 3 Marian Smoluchowski Institute of Physics, Jagiellonian University,\n30059 Krakow, Poland\nIn view of the recently increased experimental activity in the \ufb01eld of\ngraphene quantum dots [1-2], the need of a theoretical description of\nthese systems is apparent. In this work we study the symmetry classes\nof open and closed graphene quantum dots through the conductance\nand energy level statistics [3]. For an abrupt lattice termination, these\nproperties are well described by the standard orthogonal and unitary\nensembles of random matrix theory. For a smooth mass con\ufb01nement,\nthe Hamiltonian and the scattering matrix are block diagonal in the\nvalley degree of freedom. While the e\ufb00ect of this structure is clearly\nvisible in the conductance of open dots, it is suppressed in the spec-\ntral statistics of closed dots, because the intervalley scattering time is\nshorter than the time required required to resolve a level spacing in the\nclosed systems but longer than the escape time of the open systems.\n[1] L.A. Ponomarenko et. al., Science 320, 356 (2008)\n[2] C. Stampfer, et. al., Appl. Phys. Lett. 92, 012102 (2008)\nTT 26.17\nWed 18:45\nHSZ 03\nFew electrons in magnetic graphene quantum dots \u2014\n\u00a8\n\u2022Wolfgang Hausler1,2 and Reinhold Egger1 \u2014 1 Institut f\u00a8 r\nWe consider inhomogeneous magnetic \ufb01elds to design quantum islands\non graphene structures. Following the well known case of semiconducting quantum dots we investigate two interacting electrons. Without\nfurther consideration the Dirac Hamiltonian is ill de\ufb01ned for more than\none particle. We solve this issue by projecting on positive energy states\nas physically justi\ufb01ed by the presence of a chemical potential. Results\nof relatively demanding numerical diagonalizations will be presented\nfor arti\ufb01cial graphene helium.\nTime: Wednesday 14:00\u201315:00\nTT 27.1\nLocation: HSZ 105\nWed 14:00\nHSZ 105\nVortex-vortex interaction in thin superconducting \ufb01lms \u2014\nStuttgart\nThe interaction between Pearl vortices in thin superconducting \ufb01lms\nis revisited. For in\ufb01nitely extended \ufb01lms this problem was solved by\nJudea Pearl [1] who obtained the sheet current J(r) around the vortex\nand the force \u03a60 J(r) on a second vortex with magnetic \ufb02ux \u03a60 and\nat distance r in terms of the two rarely used Bessel functions S1 and\nN1 . It is shown that the interaction potential V (r) and force \u2212V (r)\ncan be approximated with high precision in the entire range of r by\na simple logarithm. This expression directly shows the correct limits\nV (r) = (\u03a62 \/\u00b50 ) ln(2.27\u039b\/r)\/(2\u03c0\u039b) for r\n\u039b and V (r) = \u03a62 \/(\u00b50 \u03c0r)\n0\n0\nfor r\n\u039b. Here \u039b = \u03bb2 \/d is the e\ufb00ective penetration depth, \u03bb the\nLondon depth, and d < \u03bb the \ufb01lm thickness. The e\ufb00ect of \ufb01nite \ufb01lm\nsize on the vortex interaction is discussed. The interaction now depends not only on the distance r but on both vortex positions and on\nthe \ufb01lm shape [2]. It is shown how the vortex interaction in \ufb01nite \ufb01lms\nof any shape and size can be computed.\n[1] J. Pearl, Appl. Phys. Lett. 5, 65 (1964).\nTT 27.2\nWed 14:15\nHSZ 105\nIntrinsic bulk vortex lattice dynamics and tilt moduli revealed by time resolved small angle neutron scattering. \u2014\n\u00a8\n\u00a8\n\u00a8\nII, D-85748 Garching \u2014 3 Institut Laue Langevin, ILL, Grenoble,\nFrance \u2014 4 School of Physics and Astronomy, University of Birmingham, Birmingham UK \u2014 5 IFW Dresden, D-01069 Dresden,\nIn contrast to the local elasticity of crystal lattices, the elasticity of\nVortex Lattices (VL) in superconductors is of non-local origin. The\nVL elasticity, thermal stability, pinning and transport properties can\nbe described by the temperature, \ufb01eld and k-dependent elastic moduli\nc11 , c44 and c66 , hence yielding important informations on the microscopic nature of superconductivity. Measurements of the VL elastic\nmoduli are traditionally limited to macroscopic transport measurements on bulk samples or microscopic surface sensitive methods such\nas decoration techniques. We report on a new method to measure\nthe VL tilt modulus c44 by means of stroboscopic small angle neutron\nscattering, combined with a time varying magnetic \ufb01eld setup on an\nultrapure niobium single crystal with vanishing pinning. This method\nallows the microscopic determination of the intrinsic VL elastic moduli\nin large bulk samples, unhampered by surface e\ufb00ects. We present \ufb01rst\ndata, showing a clear change of the vortex-vortex interaction at the\ntransition from the intermediate mixed state to the mixed state.\nTT 27.3\nWed 14:30\nHSZ 105\nInterplay of thermomagnetic and nonequilibrium e\ufb00ects in\nnonlocal vortex transport in mesoscopic NbGe channels\n\u00b4\ns\u00b4\n\u00a8\nSurgers4 , and Christoph Strunk1 \u2014 1 Inst. for Exp. and Appl.\nPhysics, Univ. Regensburg, Germany \u2014 2 Fac. of Nat. Sciences,\nUniv. of Split, Croatia \u2014 3 Dept. Physics, Univ. Zagreb, Croatia \u2014\n4 Phys. Inst. and DFG CFN, Univ. Karlsruhe, Germany\nAmorphous Nb0.7 Ge0.3 , a high-\u03ba type-II superconductor with very low\npinning, allows for measurements in the \ufb02ux-\ufb02ow regime over large\nparts of the B-T-phase diagram. When a transport current is driven\nthrough a narrow wire (width 250 nm) connected to remote voltage\nprobes via a perpendicular channel (length 2 \u00b5m) in presence of an external (out-of-plane) magnetic \ufb01eld, the Transversal Flux Transformer\nE\ufb00ect can be used to produce a nonlocal voltage drop on the remote\ncontacts caused by vortex motion in the channel. In the simplest\npicture, the Lorentz force acting on the vortices in the local wire creates a pressure on the vortices in the channel, such that the mutual\nvortex repulsion can explain the nonlocal vortex motion. However,\ndetailed measurements of nonlocal DC voltage-current characteristics\ntaken across the whole B-T-plane show several new aspects, including\nabrupt sign reversals of the vortex motion. This can be understood in\nterms of an interplay between Lorentz force (low currents) and Nernst\ne\ufb00ect via local electron heating (high currents) for T\nTc , and between the Lorentz force (low currents) and a force due to the local\nsuppression of the superconducting gap (high currents) for T close to\nTc .\nTT 27.4\nWed 14:45\nHSZ 105\nObservation of nanostripes and -clusters in NEG superconductors \u2014 \u2022Michael R. Koblischka1 , Marc Winter1 ,\nThomas Wolf4 , Nadendla Hari Babu5 , Steve Turner6 , Gustav\nvan Tendeloo6 , and Uwe Hartmann1 \u2014 1 Experimental Physics,\nSaarland University, Campus C 6 3, D-66123 Saarbr\u00a8cken, Germany\n\u2014 2 Functional Materials, Saarland University, Campus C 6 3, D-66123\nSaarbr\u00a8cken, Germany \u2014 3 SRL\/ ISTEC, 1-10-13, Shinonome, Kotou\nInstitute of Solid State Physics, D-76021 Karlsruhe, Germany \u2014 5 IRC\nin Superconductivity, University o","kit-publication-id":"230075161"}]