Identification and Characterization of Two Energy Gaps in Superconducting MgB2 by Specific-Heat Measurements

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This paper reports specific-heat measurements on superconducting MgB2 in magnetic fields to 9 T. In zero magnetic field the data can be fitted to a two-gap model, which is a generalization of a semi-empirical model for strong-coupled, single-gap superconductors (the alpha-model), to within the precision of the data. Both gaps close at Tc, with one gap larger and one smaller than the BCS weak-coupling-limit. (The two gaps have a ratio 4:1.) Each gap accounts for 50% of the normal electron density of states. The parameters characterizing the fits agree well with those from recent spectroscopic measurements and theory. In magnetic fields the superconductong anomaly is broadened as expected for an anisotropic, randomly-oriented superconductor.