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

TL;DR

This study systematically characterizes the upper critical fields of MgB$_2$ thin films using two-band superconductivity theory, revealing correlations with transition temperature and analyzing transition width anomalies.

Contribution

It provides a comprehensive analysis of $H_{c2}$ in MgB$_2$ films with experimental data fitted to the two-band superconductivity model, highlighting the relationship with $T_c$.

Findings

Parameters from the model correlate with $T_c$.

Successful analysis of $H_{c2}(T)$ data using Gurevich theory.

Observation of anomalous transition width narrowing at intermediate temperatures.

Abstract

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.