Systematic characterization of upper critical fields for MgB$_2$ thin   films using the two-band superconducting theory
  We present experimental results of the upper critical fields $H_{\rm c2}$ of various MgB$_2$ thin films prepared by the molecular beam epitaxy, multiple-targets sputtering, and co-evaporation deposition apparatus. Experimental data of the $H_{\rm c2}(T)$ are successfully analyzed by applying the Gurevich theory of dirty two-band superconductivity in the case of $D_{\pi}/D_{\sigma}>1$, where $D_{\pi}$ and $D_{\sigma}$ are the intraband electron diffusivities for $\pi$ and $\sigma$ bands, respectively. We find that the parameters obtained from the analysis are strongly correlated to the superconducting transition temperature $T_{\rm c}$ of the films. We also discuss the anormalous narrowing of the transition width at intermediate temperatures confirmed by the magnetoresistance measurements. 
S. Noguchi, A. Kuribayashi, T. Ishida, T. Oba, H. Iriuda, M.   Yoshizawa, Y. Harada, S. Miki, H. Shimakage, Z. Wang, K. Sato...