Specific heat of single crystal MgB_2: a two-band superconductor with   two different anisotropies
  Heat-capacity measurements of a 39 microgramm MgB_2 single crystal in fields up to 14 T and below 3 K allow the determination of the low-temperature linear term of the specific heat, its field dependence and its anisotropy. Our results are compatible with two-band superconductivity, the band carrying the small gap being isotropic, that carrying the large gap having an anisotropy of ~ 5. Three different upper critical fields are thus needed to describe the superconducting state of MgB2. 
F. Bouquet, Y. Wang, I. Sheikin, T. Plackowski, A. Junod, S. Lee, S.   Tajima