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Point-Contact Andreev-Reflection Spectroscopy in the Fe-based Superconductor LaFeAsO1−x F x

  • M. Tortello
  • D. Daghero
  • G. A. Ummarino
  • R. S. Gonnelli
  • V. A. Stepanov
  • J. S. Kim
Open Access
Original Paper

Abstract

Point-contact Andreev-reflection (PCAR) spectroscopy measurements have been performed in the Fe-based superconductor LaFeAsO1−x F x in order to investigate the energy gaps. The Andreev spectra show clear and reproducible features that could be related to two nodeless gaps. Their values, as determined by fitting the conductance curves measured in junctions with local T c =27.3–28.6 K within the two-band BTK model, are Δ 1=2.75–3.8 meV for the small gap and Δ 2=7.9–10.2 meV for the larger one, respectively. The absence of zero-bias conductance peaks and considerations regarding the nonperfectly directional current injection in PCAR experiments and the polycrystalline nature of the samples rule out the possibility of nodal gaps in the superconductor. Moreover, the conductance curves show pseudogap-like features coexisting, at low temperature, with superconductivity and disappearing close to the Néel temperature of the parent compound, T N≈140 K.

Keywords

Fe-based superconductors Point-contact Andreev-reflection spectroscopy Energy gaps Iron pnictides 

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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • M. Tortello
    • 1
  • D. Daghero
    • 1
  • G. A. Ummarino
    • 1
  • R. S. Gonnelli
    • 1
  • V. A. Stepanov
    • 2
  • J. S. Kim
    • 3
  1. 1.Dipartimento di Fisica and CNISMPolitecnico di TorinoTurin (TO)Italy
  2. 2.P.N. Lebedev Physical InstituteRussian Academy of SciencesMoscowRussia
  3. 3.Max-Planck-Institut für FestkörperforschungStuttgartGermany

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