[{"type":"speech","title":"Interband pairing interaction in the two-band superconductor MgB\u2082 observed by tunneling","issued":{"date-parts":[["2005"]]},"author":[{"family":"Geerk","given":"J."},{"family":"Schneider","given":"R."},{"family":"Linker","given":"G."},{"family":"Zaitsev","given":"A."},{"family":"Heid","given":"R."},{"family":"Bohnen","given":"K. P."},{"family":"Loehneysen","given":"H. von"}],"note":"Physik seit Albert Einstein : 69.Jahrestagung der DPG, Berlin, 4.-9.M\u00e4rz 2005 Verhandlungen der Deutschen Physikalischen Gesellschaft, R.6, B.40(2005) TT 18.2","abstract":"TT 18.2 Mo 10:30 TU H2053\nInterband Pairing Interaction in the Two-Band Superconductor MgB2 Observed by Tunneling \u2014 \u2022J. Geerk1 , R. Schneider1 , G. Linker1 , A. Zaitsev1 , R. Heid1 , K.-P. Bohnen1 , and\nstitut, Universit\u00a8t Karlsruhe\nThe anisotropic superconductor MgB2 was studied by tunneling spectroscopy of tunnel junctions of the sandwich type prepared on as deposited thin \ufb01lms with Tc values near 32 K. The tunnel junctions revealed\nan energy gap between 2.5 and 3 meV and phonon induced structures in\nthe tunnelling density of states. The inversion of the tunnel data using\nthe standard single-band Eliashberg equations yielded a so-called e\ufb00ective Eliashberg function with three distinct peaks at 38,58 and 85 meV\nwhich is compared to a theoretical calculated counterpart obtained by inversion of superconducting density of states data from two-band Eliashberg equations where electron-phonon spectral functions extracted from\nab-initio LDA calculations were inserted. Convincing agreement is found\nbetween the experimental and calculated e\ufb00ective Eliashberg functions.\nFurther evaluation reveals that the central peak a 58 meV mainly re\ufb02ects\nthe shape of the \u03c0-\u03c3 interband pairing interaction which appears in the\ngap function of the \u03c0-sheet in an ampli\ufb01ed way due to the large gap of\nthe \u03c3-sheet. It is concluded that the superconductivity on the \u03c0-sheet is\nessentially generated by interband electron-phonon coupling.\nTT 18.3 Mo 10:45 TU H2053\nMixing between ballistic and di\ufb00usive motion in superconducting MgB2 \u2014 \u2022Matthias Eschrig1 , Kaori Tanaka2,3 ,\nFestk\u00a8rperphysik, Universit\u00a8t Karlsruhe, 76128 Karlsruhe, Germany\n\u2014 2 Department of Physics and Engineering Physics, University of\nSaskatchewan, Saskatoon, SK, Canada S7N 5E2 \u2014 3 Argonne National\nLaboratory, Argonne, IL 60439, U.S.A. \u2014 4 Department of Physics,\nUniversity of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI\n53211, U.S.A \u2014 5 Low Temperature Laboratory, Helsinki University of\nTechnology, PO Box 2200, FIN-02015 HUT\nWe introduce a model for the two-band superconductor MgB2 in which\nthe motion of quasiparticles is di\ufb00use in one band (the \u03c0-band) and ballistic in the other band (the \u03c3-band). Di\ufb00usive and ballistic quasiparticles\nare coupled by the pairing interaction. We apply this model to examine\nthe electronic structure of vortex cores in MgB2 . In particular, we study\nthe e\ufb00ects of impurities on the ballistic motion of quasiparticles in the\n\u03c3-band in the vortex core region under the presence of the hybridization\nwith the di\ufb00usive \u03c0-band.We \ufb01nd that the induced superconductivity in\nthe \u03c0 band results in a core size larger than estimated by HC2 and in\nweakly bound states, and that those bound states are removed easily by\nimpurities.\nTT 18.4 Mo 11:00 TU H2053\nBand \ufb01lling and interband scattering e\ufb00ects in MgB2 : C vs\nAl doping \u2014 \u2022Jens Kortus1 , O.V. Dolgov2 , R.K. Kremer2 , and\nA.A. Golubov3 \u2014 1 Institut de Physique et Chimie des Mat\u00b4riaux de\nStrasbourg, 23 rue du Loess, F-67034 Strasbourg Cedex 2, France \u2014\n2\nMPI-FKF, Heisenbergstr. 1, 70569 Stuttgart \u2014 3 MESA+ Research Institute and Faculty of Science and Technology, University of Twente,\n7500 AE Enschede, The Netherlands\nWe argue, based on band structure calculations and Eliashberg theory,\nthat the observed decrease of Tc of Al and C doped MgB2 samples can\nbe understood mainly in terms of a band \ufb01lling e\ufb00ect due to the electron\ndoping by Al and C. A simple scaling of the electron-phonon coupling\nconstant \u03bb by the variation of the density of states as function of electron doping is su\ufb03cient to capture the experimentally observed behavior.\nFurther, we also explain the long standing open question of the experimental observation of a nearly constant \u03c0 gap as function of doping by a\ncompensation of the e\ufb00ect of band \ufb01lling and interband scattering. Both\ne\ufb00ects together generate a nearly constant \u03c0 gap and shift the merging\npoint of both gaps to higher doping concentrations, resolving the discrepancy between experiment and theoretical predictions based on interband\nscattering only.\nMontag\nTT 18.5 Mo 11:15 TU H2053\nDensity functional theory for superconductors: Applications to\nMgB2 and solids under pressure \u2014 \u2022Andrea Floris1 , Cesare\nFranchini2 , Nektarios Lathiotakis1 , Gianni Profeta3 , Sandro\nMassidda2 , and E. K. U. Gross1 \u2014 1 Institut f\u00a8r Theoretische Physik,\nFreie Universit\u00a8t Berlin, Germany \u2014 2 INFM SLACS, Sardinian Laboraa\ntory for Computational Materials Science and Dipartimento di Scienze\nFisiche, Universit` degli Studi di Cagliari, Italy \u2014 3 C. A. S. T. I. - Istia\ntuto Nazionale Fisica della Materia (INFM) and Dipartimento di Fisica,\nUniversit` degli studi dell\u2019 Aquila, Italy\nUnderstanding and predicting the properties of superconductors is of\nboth fundamental and technological importance. The discovery of superconductivity in MgB2 , of its rather high critical temperature (Tc =\n39.5K), and the appearance of multiple gaps, has renewed the interest\nin conventional superconductivity. Here we present several applications\nof a novel approach to superconductivity that allows one to calculate\nmaterial-speci\ufb01c properties, such as the gap and the Tc , in a truly abinitio fashion without using any adjustable parameters. Within this approach, we obtained the Tc and the two gaps of MgB2 in good agreement\nwith experiment, taking into account the strong anisotropy of both the\nelectron-phonon and the Coulomb interactions. As a further application,\nwe studied the behaviour of Tc in Li and Al as a function of pressure. Despite their common simple metal structure, these materials show di\ufb00erent\nbehaviour upon pressure. While Li undergoes several transitions favouring superconductivity, in Al the electron-phonon coupling decreases with\npressure leading to a complete suppression of Tc around 8GPa.\nTT 18.6 Mo 11:30 TU H2053\nMulti-band in\ufb02uence on superconductivity in HoNi2 B2 C \u2014\n\u2022A. W\u00a8lte1 , G. Fuchs1 , Yu.G. Naidyuk2 , K. Nenkov1 , S.-L.\nDrechsler1 , D. Souptel1 , H. Rosner3 , J. Freudenberger1 , K.H. M\u00a8ller1 , G. Behr1 , and L. Schultz1 \u2014 1 Institut f\u00a8r Festk\u00a8rperu\n2\nB. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 47 Lenin Ave., 61103 Kharkiv,\nRare-earth nickel borocarbides RNi2 B2 C reveal, depending on the rareearth R, superconductivity, magnetism or even a mixture of these competing phenomena [1]. The reduction of the superconducting ordering\ntemperature Tc by magnetic pair-breaking fairly follows the AbrikosovGorkov model. However, details of the in\ufb02uence of magnetism on the\nelectron system are not yet well understood. From speci\ufb01c heat measurements and point-contact spectroscopy on HoNi2 B2 C the phonon density\nof states F (\u03c9) and the spectral function \u03b12 F (\u03c9) have been extracted.\nThe characteristic phonon frequency \u03c9ln \u2248 180 K is similar to \u03c9ln of nonmagnetic LuNi2 B2 C. Comparing the speci\ufb01c heat jumps of both compounds, an unexpectedly strong deviation from the Abrikosov-Gorkov\nexpectation for HoNi2 B2 C is found. A possible explanation is the di\ufb00erent in\ufb02uence of pair-breaking on di\ufb00erent electron bands.\n[1] R.J. Cava et al., Nature 367, January 1994.\nTT 18.7 Mo 11:45 TU H2053\nAre intercalated metallochloronitrides electron-phonon mediated superconductors? \u2014 \u2022Rolf Heid and Klaus-Peter Bohnen\nThe layered metallochloronitrides XNCl, X=Zr,Hf, have surprised with\nrather high superconducting transition temperatures of up to 25.5 K after intercalation with Li or Na [1], raising the question to what extent\nthe conventional electron-phonon coupling mechanism is at work. Here\nwe present results of an ab in","kit-publication-id":"230060653"}]