Systematic characterization of upper critical fields for MgB${}_2$ thin films using the two-band superconducting theory

Abstract

We present experimental results of the upper critical fields $H_{c2}$ of various MgB${}_2$ thin films prepared by the molecular beam epitaxy, multiple-targets sputtering, and co-evaporation deposition apparatus. Experimental data of the $H_{c2}(T)$ are successfully analyzed by applying the Gurevich theory of dirty two-band superconductivity in the case of $D_{\ddot{I}}€/D_{\ddot{I}}ƒ>1$, where $D_{\ddot{I}}€$ and $D_{\ddot{I}}ƒ$ are the intraband electron diffusivities for $\ddot{I}€$ and $\ddot{I}ƒ$ bands, respectively. We find that the parameters obtained from the analysis are strongly correlated to the superconducting transition temperature $T_{\mathrm{c}}$ of the films. We also discuss the anormalous narrowing of the transition width at intermediate temperatures confirmed by the magnetoresistance measurements.

7 pages, 7 figures, submitted to Phys. Rev. B