Abstract:
Using tunneling spectroscopy of planar “break-junctions” we show a multiple-gap superconductivity in CaKFe$_4$As$_4$ pnictides. We determine the magnitudes and temperature dependences of the microscopic superconducting order parameter $\Delta_i(T)$. The temperature dependences of the features caused by Andreev transport are obtained: Andreev excess current $I_{\mathrm{exc}}(T)$ and Andreev zero-bias conductance $G_{\mathrm{ZBC}}^{\mathrm{A}}(T)$. As well, the temperature dependence of the critical current $I_{\mathrm{c}}(T)$ is measured. Using data of $I_{\mathrm{exc}}(T)$, $G_{\mathrm{ZBC}}^{\mathrm{A}}(T)$, and $I_{\mathrm{c}}(T)$, we estimate the partial conductance of the two effective bands, and show the dominate contribution of the “driving” bands with the large superconducting gap to the total conductance.
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