Andreev reflection spectroscopy evidence for multiple gaps in MgB 2
2002; American Physical Society; Volume: 66; Issue: 6 Linguagem: Inglês
10.1103/physrevb.66.064513
ISSN1095-3795
AutoresZhuangzhi Li, Hongjie Tao, Yi Xuan, Zhi-An Ren, Guangcan Che, Bairu Zhao,
Tópico(s)Physics of Superconductivity and Magnetism
ResumoAndreev reflection tunneling spectroscopy on ${\mathrm{MgB}}_{2}/\mathrm{PtIr}$ point contacts have systematically been investigated. By fitting tunneling conductance to Blonder-Tinkham-Klapwijk theory, s-wave superconducting gaps were obtained. The distribution of the obtained gaps unequivocally shows two groups: one centered at 9.8 meV and the other peaked at 2.8 meV with a gap ratio of 3.5. For two typical gaps ${\ensuremath{\Delta}}_{1}=1.92 \mathrm{meV}$ and ${\ensuremath{\Delta}}_{2}=3.45 \mathrm{meV}$ their temperature-dependent behavior display that ${\ensuremath{\Delta}}_{1}(T)$ unambiguously persists to the bulk ${T}_{c},$ 39 K, and ${\ensuremath{\Delta}}_{2}(T)$ closes at 33 K. The results support multigap scenarios; in addition our experiments yield a much higher value of the large gap than the previous reports and theoretical predictions, indicating there may exist even stronger electron-phonon coupling in ${\mathrm{MgB}}_{2}.$
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