Berlin 2005 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 23: Posters Superconductivity, Solids at Low Temperature
TT 23.32: Poster
Montag, 7. März 2005, 14:00–18:00, Poster TU D
Observation of a second energy gap in Nb3Sn — •M. Marz1, R. Lortz2, A. Junod2, W. Goldacker3, and G. Goll1 — 1Physikalisches Institut, Universität Karlsruhe, D-76128 Karlsruhe, Germany — 2Department of Condensed Matter Physics, University of Geneva, CH-1211 Geneva 4, Switzerland — 3Forschungszentrum Karlsruhe, Institut für Technische Physik, D-76021 Karlsruhe, Germany
Nb3Sn is a well-known technically applied superconductor with critical temperature Tc≈ 18 K. Recently, a low-temperature anomaly in the specific-heat data on a particularly dense and homogeneous polycrystalline sample has been interpreted in terms of the presence of a second superconducting gap [1]. We performed point-contact spectroscopy on samples of the same batch using the break-junction technique. A small bar of Nb3Sn has been broken at liquid-helium temperature in order to obtain a freshly cleaved surface. We measured the differential resistance as a function of applied voltage in the temperature range between 1.5 and 20 K. Several characteristic minima in the dV/dI vs V curves can be interpreted only under the assumption of two superconducting energy gaps in Nb3Sn. From a comparison with calculated curves for superconductor-superconductor contacts we deduced a large gap ΔL=3.5± 0.2 meV and a small gap of ΔS=0.8± 0.2 meV. This is the first spectroscopic confirmation of two-gap superconductivity in Nb3Sn. We note that ΔL is in line with previous tunnelling measurements and the result confirms the interpretation of the specific-heat data.
[1] V. Guritanu et al., Phys. Rev. B (2004) in print.