Coherence lengths and anisotropy in MgB2 superconductor
  Field and temperature microwave measurements have been carried out on MgB2 thin film grown on Al2O3 substrate. The analysis reveals the mean field coherence length xi_{MF} in the mixed state and a temperature independent anisotropy ratio gamma_{MF} = xi_{MF}^{ab} / xi_{MF}^c approximately 2. At the superconducting transition, the scaling of the fluctuation conductivity yields the Ginzburg-Landau coherence length with a different anisotropy ratio gamma_{GL} = 2.8, also temperature independent. 
A. Dulcic, M. Pozek, D. Paar, Eun-Mi Choi, Hyun-Jung Kim, W.N. Kang,   Sung-Ik Lee