Journal of Superconductivity and Novel Magnetism

, Volume 26, Issue 9, pp 2867–2871 | Cite as

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

  • Y. G. Ponomarev
  • S. A. Kuzmichev
  • T. E. Kuzmicheva
  • M. G. Mikheev
  • M. V. Sudakova
  • S. N. Tchesnokov
  • O. S. Volkova
  • A. N. Vasiliev
  • V. M. Pudalov
  • A. V. Sadakov
  • A. S. Usol’tsev
  • T. Wolf
  • E. P. Khlybov
  • L. F. Kulikova
Original Paper

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 .

Keywords

Fe-based superconductors Two-gap superconductivity Multiple Andreev reflections Subharmonic gap structure Break-junction 

Notes

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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Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  • Y. G. Ponomarev
    • 1
  • S. A. Kuzmichev
    • 1
  • T. E. Kuzmicheva
    • 1
    • 2
  • M. G. Mikheev
    • 1
  • M. V. Sudakova
    • 1
  • S. N. Tchesnokov
    • 1
  • O. S. Volkova
    • 1
  • A. N. Vasiliev
    • 1
  • V. M. Pudalov
    • 2
  • A. V. Sadakov
    • 2
  • A. S. Usol’tsev
    • 2
  • T. Wolf
    • 3
  • E. P. Khlybov
    • 4
  • L. F. Kulikova
    • 4
  1. 1.Lomonosov Moscow State UniversityMoscowRussia
  2. 2.Lebedev Physical Institute RASMoscowRussia
  3. 3.Karlsruher Institut für TechnologieInstitut für FestkörperphysikKarlsruheGermany
  4. 4.Institute for High Pressure Physics RASTroitskRussia

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