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Superconducting energy gap distribution in c-axis oriented MgB$_2$ thin film from point contact study

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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Abstract

We have analyzed about 100 voltage-dependent differential resistance dV/dI(V) curves of metallic point contacts between c-axis oriented MgB$_2$ 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 a single-gap features result in 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 $Δ_{S}=2.45\pm 0.15$ meV and $Δ_{L}=7.0\pm 0.45$ meV in MgB$_2$ with gap ratio $2.85\pm 0.15$. Our observations prove further a widely discussed multi-gap scenario for MgB$_2$, 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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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. 2002-03-30. Superconducting energy gap distribution in c-axis oriented MgB$_2$ thin film from point contact study. https://doi.org/10.1134/1.1478521

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