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 $D_{\pi }/D_{\sigma }>1$, 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 $T_{\mathrm{c}}$ 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

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