Heat-capacity measurements of a 39μg MgB2 single crystal in fields up to 14T and below 3K allow the determination of the low-temperature linear term of the specific heat, its field dependence, and its anisotropy. The results were compatible with 2-band superconductivity, the band carrying the smaller gap being isotropic, that carrying the larger gap having an anisotropy of approximately 5. Three different upper critical fields were thus needed to describe the superconducting state of MgB2.

Specific Heat of Single Crystal MgB2 - a Two-Band Superconductor with Two Different Anisotropies. F.Bouquet, Y.Wang, I.Sheikin, T.Plackowski, A.Junod, S.Lee, S.Tajima: : Physical Review Letters, 2002, 89[25], 257001 (3pp)