Multiple Andreev Reflections Spectroscopy of Two-Gap 1111- and 11 Fe-Based Superconductors

• Published in: Journal of superconductivity and novel magnetism 2013-09, Vol.26 (9), p.2867-2871
• Main Authors: Ponomarev, Y. G., Kuzmichev, S. A., Kuzmicheva, T. E., Mikheev, M. G., Sudakova, M. V., Tchesnokov, S. N., Volkova, O. S., Vasiliev, A. N., Pudalov, V. M., Sadakov, A. V., Usol’tsev, A. S., Wolf, T., Khlybov, E. P., Kulikova, L. F.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Gaps; Magnetic Materials; Magnetism; Original Paper; Physics; Physics and Astronomy; Strongly Correlated Systems; Superconductivity
• ISSN: 1557-1939; 1557-1947
• DOI: 10.1007/s10948-013-2264-7

Using the “break-junction” technique, we prepared and studied superconductor–constriction–superconductor (ScS) nanocontacts in polycrystalline samples of Fe-based superconductors CeO 0.88 F 0.12 FeAs (Ce-1111; ), LaO 0.9 F 0.1 FeAs (La-1111; ), and FeSe ( ). We detected two subharmonic gap structures related with multiple Andreev reflections, indicating the presence of two superconducting gaps with the BCS-ratios 2 Δ L / k B T C =4.2÷5.9 and 2 Δ 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 ≈2 Δ L .