title: Disorder effects in pnictides: a tunneling spectroscopy study.
abstract: We present the synthesis and the tunneling spectroscopy study of superconducting FeSe(0.5)Te(0.5) (T(c) = 14 K), SmFeAsO(0.85) (T(c) = 54 K) and SmFeAsO(0.9)F(0.1) (T(c) = 45 K). The samples were characterized by Rietveld refinement of x-ray diffraction patterns and transport as well as temperature-dependent magnetic measurements. Tunneling experiments on FeSe(0.5)Te(0.5) revealed a single superconducting gap ∼ 1 meV in BCS-like tunneling conductance spectra. In SmFeAsO(0.85) and SmFeAsO(0.9)F(0.1), however, more complex spectra were observed, characterized by two gap-like structures at ∼ 4 and ∼ 10 meV. These spectra are qualitatively understood assuming a two-band superconductor with a 's ±' order parameter. We show that, depending on the sign relation between the pairing amplitudes in the two bands, the interband quasiparticle scattering has a crucial effect on the shape of the tunneling spectra. On the other hand, single-gap spectra found in FeSe(0.5)Te(0.5) are more compatible with a disorder-induced 's '-wave gap, due to the Se-Te substitution.
authors.affiliation: Institut des Nanosciences de Paris, CNRS UMR 7588, Université Pierre et Marie Curie Paris 6, Paris, France. yves.noat@insp.jussieu.fr
authors.forename: Y
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authors.lastname: Noat
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authors.lastname: Cren
authors.forename: V
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authors.lastname: Dubost
authors.forename: S
authors.initials: S
authors.lastname: Lange
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authors.initials: F
authors.lastname: Debontridder
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authors.lastname: Toulemonde
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authors.initials: J
authors.lastname: Marcus
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authors.lastname: Sulpice
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authors.lastname: Sacks
authors.forename: D
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authors.lastname: Roditchev