Abstract
Using the “break-junction” technique, we prepared and studied superconductor–constriction–superconductor (ScS) nanocontacts in polycrystalline samples of Fe-based superconductors CeO0.88F0.12FeAs (Ce-1111; \(T_{C}^{\mathrm{bulk}} = 41 \pm1~\mathrm{K}\)), LaO0.9F0.1FeAs (La-1111; \(T_{C}^{\mathrm{bulk}} = 28 \pm1~\mathrm {K}\)), and FeSe (\(T_{C}^{\mathrm{bulk}} = 12 \pm1~\mathrm{K}\)). We detected two subharmonic gap structures related with multiple Andreev reflections, indicating the presence of two superconducting gaps with the BCS-ratios 2Δ L /k B T C =4.2÷5.9 and 2Δ S /k B T C ∼1≪3.52, respectively. Temperature dependences of the two gaps Δ L,S (T) in FeSe indicate a k-space proximity effect between two superconducting condensates. For the studied iron-based superconductors, we found a linear relation between the gap Δ L and magnetic resonance energy, E res≈2Δ L .
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Acknowledgements
The work was supported by the Russian Ministry of Education and Sciences (contract 11.519.11.60.12, grant 8375), RFBR (grants 12-02-31269, 13-02-01451), DFG Grants 436RUS113 and FOR 538/BU887/4, and DFG priority program (SPP1458). We thank T. Hänke, C. Hess, G. Behr, R. Klingeler, and B. Büchner for the La-1111 samples synthesis.
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Ponomarev, Y.G., Kuzmichev, S.A., Kuzmicheva, T.E. et al. Multiple Andreev Reflections Spectroscopy of Two-Gap 1111- and 11 Fe-Based Superconductors. J Supercond Nov Magn 26, 2867–2871 (2013). https://doi.org/10.1007/s10948-013-2264-7
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DOI: https://doi.org/10.1007/s10948-013-2264-7