English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We studied iron-based superconductors of various families with criticaltemperatures covering almost all range $T_C = 9 - 53$ K. In natural arrays ofcontacts formed in these materials we observed intrinsic multiple Andreevreflections effect (IMARE). By using IMARE spectroscopy, we detected thetwo-gap superconductivity, determined the value of the large and the smallsuperconducting gaps, and the corresponding BCS-ratios. The temperaturedependencies of the large and the small gaps $\Delta_{L,S}(T)$ are similar forvarious families of the Fe-based superconductors and could be well-fitted inthe framework of the two-band model by Moskalenko and Suhl. We concluded on theextended s-wave symmetry of the $\Delta_L$ order parameter (20-30 % anisotropyin k-space) and on the absence of nodes for $\Delta_S$. The BCS-ratio$2\Delta_L/k_BT_C \approx 5.2$ is nearly constant within the whole range of$T_C$ (this means that coupling rate is unchanged), reflecting the 20 %reduction of the $T_C^{local}$ in relation to the eigen $T_C^L$, and the largegap roughly corresponds to the energy of magnetic resonance $2\Delta_L \approxE_{res}$. This result requires a special theoretical consideration. Ourestimation of the relative coupling constants and eigen parameters of eachcondensate (in a hypothetical case of a zero interband interaction)$2\Delta_L/k_BT_C^L = 4.2 - 4.8$ and $2\Delta_S/k_BT_C^S = 3.5 - 4.5$ leads toindirect conclusion that namely a strong electron-phonon interaction in eachcondensate described in the framework of the Eliashberg theory plays the keyrole in the superconductivity of iron-based oxypnictides. With it, the twocondensates interact weakly with each other. The observed scaling of$\Delta_{L,S}$ with $T_C$, as was discussed above, is caused mainly by changingof the density of states $N_{L,S}$ in the bands, whereas Ln-O spacers act ascharge reservoirs.

Andreev spectroscopy of iron-based superconductors: temperature dependence of the order parameters and scaling of the $\Delta_{L,S}$ with $T_C$