Superconducting energy gap distribution in c-axis oriented MgB2 thin film from point contact study |
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Authors: | Yu G Naidyuk I K Yanson L V Tyutrina N L Bobrov P N Chubov W N Kang Hyeong-Jin Kim Eun-Mi Choi Sung-Ik Lee |
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Institution: | (1) Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, Kharkiv, 61103, Ukraine;(2) National Creative Research Initiative Center for Superconductivity, Department of Physics, Pohang University of Science and Technology, 790-784 Pohang, South Korea |
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Abstract: | We have analyzed about a hundred voltage-dependent differential resistance dV/dI(V) curves of metallic point contacts between c-axis-oriented MgB2 thin film and Ag, which exhibit clear Andreev reflection features connected with the superconducting gap. About one half of the curves show the presence of a second larger gap. The histogram of the double gap distribution reveals distinct maxima at 2.4 and 7 meV, while curves with single-gap features result in a more broad maximum at 3.5 meV. The double-gap distribution is in qualitative agreement with the distribution of gap values over the Fermi surface calculated by H. J. Choi et al. (cond-mat/0111183). The data unequivocally show the presence of two gaps: ΔS=2.45±0.15 meV and ΔL=7.0±0.45 meV in MgB2 with the gap ratio ΔL/ΔS=2.85±0.15. Our observations further prove a widely discussed multigap scenario for MgB2, where two distinct gaps are seen in the clean limit, while a single averaged gap is present in the dirty one. |
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