Controversial tunnel and point-contact experimental data on superconducting gap values in MgB2 were analyzed and interpreted in terms of the spatial inhomogeneity and the proximity effect appropriate to this layered compound. Existing specific heat measurements were explained in the same way. Break-junction tunnel studies of polycrystalline MgB2 samples were carried out and a clear-cut multiplicity of gaps was observed, although the shapes of the I–V characteristics vary substantially.

Spatially Heterogeneous Character of Superconductivity in MgB2 as Revealed by Local Probe and Bulk Measurements. T.Ekino, A.M.Gabovich, M.S.Li, T.Takasaki, A.I.Voitenko, J.Akimitsu, H.Fujii, T.Muranaka, M.Pekala, H.Szymczak: Physica C, 2005, 426-431[1], 230-3