Multiple-Gap Features from Break-Junction Tunneling in the Superconducting MgB_2(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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Tunneling spectroscopy measurements on polycrystalline MgB_2 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 Δ_S = 2.2 ± 0.3 meV, Δ_M = 6.0 ± 1.5 meV, and Δ_L ≅ 10 meV. All these gaps exist up to the same critical temperature T_c. The Δ_M 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-T_c phases. Our tunneling data can be explained by the proximity effect combined with the bulk multiple-gap features.
社団法人日本物理学会の論文
2004-07-15