Superconducting Transition and Phase Diagram of Single Crystal MgB2
  The superconducting phase diagram of MgB2 was determined from magnetization, magneto-transport and the first single-crystal specific heat measurements. A zero-temperature in-plane coherence length of 8 nm is determined. The superconducting anisotropy increases from a value around 2 near Tc to above 4.5 at 22 K. For H||c a pronounced peak effect in the critical current occurs at the upper critical field. Evidence for a surface superconducting state is presented for H||c which might account for the wide spread in reported values of the anisotropy. 
U. Welp, G. Karapetrov, W. K. Kwok, G. W. Crabtree, Ch. Marcenat, L.   Paulius, T. Klein, J. Marcus, K. H. P. Kim, C. U. Jun...