Large Broadening of the Superconducting Transition by Fluctuations in a   3D Metal at High Magnetic Fields: The MgB$_{2}$ case
  It is shown that the transition to the low temperature superconducting state in a 3D metal at high magnetic field is smeared dramatically by thermal fluctuation of the superconducting order parameter. The resulting superconducting-to-normal crossover occurs in a vortex liquid state which is extended well below the mean-field $H_{c2}$. Application to MgB$_{2}$ yields good quantitative agreement with recently reported data of dHvA oscillation in the superconducting state. 
T. Maniv and V. Zhuravlev