Physics – Condensed Matter – Superconductivity
Scientific paper
2001-12-25
JETP Letters, 2002, Vol.75, No.5, pp.238-241
Physics
Condensed Matter
Superconductivity
V1:4 pages incl. 4 figures, RevTex4. V2: version for JETP Letters, 4 pages incl 3 Figs., jetpl.cls
Scientific paper
10.1134/1.1478521
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 $\Delta_{S}=2.45\pm 0.15$ meV and $\Delta_{L}=7.0\pm 0.45$ 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.
Bobrov N. L.
Choi Eun-Mi
Chubov P. N.
Kang* Won Nam
Kim Hyeong-Jin
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