Multiple-gap features from break-junction tunneling in the superconducting MgB2

• Published in: Journal of the Physical Society of Japan 2004-07, Vol.73 (7), p.1902-1913
• Main Authors: TAKASAKI, Tomoaki, EKINO, Toshikazu, MURANAKA, Takahiro, ICHIKAWA, Takayuki, FUJII, Hironobu, AKIMITSU, Jun
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Physics; Proximity effects, weak links, tunneling phenomena, and josephson effects, adreev effect, sn and sns junctions; Superconductivity
• ISSN: 0031-9015; 1347-4073
• DOI: 10.1143/JPSJ.73.1902

Tunneling spectroscopy measurements on polycrystalline MgB2 have been carried out with a break-junction technique. The observed spectra exhibit the multiple-gap feature, which can be expressed by the correlated two-gap model. From the conductance fittings at 4.2 K, the gap parameters can be classified into δS=2.2±0.3 meV, δM=6.0±1.5 meV, and δL[congruent with]10 meV. All these gaps exist up to the same critical temperature Tc. The δM undergoes various ways of temperature dependence, which can be attributed to the proximity-induced gap. We have also observed the conductances showing the features of normal conducting and/or low-Tc phases. Our tunneling data can be explained by the proximity effect combined with the bulk multiple-gap features.