Anisotropy of the Upper Critical Field and Critical Current in Single   Crystal MgB$_2$
  We report on specific heat, high magnetic field transport and $ac-$susceptibility measurements on magnesium diboride single crystals. The upper critical field $H_{c2}$ for magnetic fields perpendicular and parallel to the Mg and B planes is presented for the first time in the entire temperature range. A very different temperature dependence has been observed in the two directions which yields to a temperature dependent anisotropy with $\Gamma \sim$ 5 at low temperatures and about 2 near $T_c$. A peak effect is observed in susceptibility measurements for $H \sim $2 T parallel to the $c-$axis and the critical current density presnts a sharp maximum for $H$ parallel to the ab-plane. 
L.Lyard, P.Samuely, P.Szabo, T. Klein, C.Marcenat, L. Paulius,   K.H.P.Kim, C.U.Jung, H.-S.Lee, B.Kang, S. Choi, S.-I.Lee, J...