Evidence for two-gap superconductivity in (Ba,K)Fe_2As_2 by directional point contact Andreev reflection spectroscopy

Abstract

Directional point-contact Andreev-reflection spectroscopy measurements on the Ba${}_{0.55}$K${}_{0.45}$Fe${}_2$As${}_2$ single crystals are presented. The spectra show significant differences when measured in the $ab$ plane in comparison with those measured in the $c$ direction of the crystal. In the latter case only a reduced point-contact conductance around zero bias has been revealed persisting well above $T_c$ and probably related to the structural and magnetic transitions in the system. Within the $ab$ plane two superconducting energy gaps are detected below $T_c$. Here a reduced conductance above $T_c$ could also be found. The fits of the $ab$-plane data to the superconducting s-wave two-gap model indicate that the smaller gap has a size below the BCS value while the large gap reveals much higher coupling strength.

published version

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Cited by in corpus (8)

• Unconventional London penetration depth in Ba(Fe0.93Co0.07)2As2 single crystals
• Momentum-resolved superconducting gap in the bulk of Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ from combined ARPES and $\mu$SR measurements
• Non-exponential London penetration depth in Ba${}_{1-}$K${}_x$Fe${}_2$As${}_2$ single crystals
• Lower Critical Fields of Superconducting PrFeAsO${}_{1-y}$ Single Crystals
• Coexistence of two order parameters and a pseudogaplike feature in the iron-based superconductor LaFeAsO_(1-x)F_x
• Point-contact Andreev-reflection spectroscopy in ReFeAsO_{1-x}F_x (Re = La, Sm): Possible evidence for two nodeless gaps
• Investigation of Superconducting Gap Structure in TbFeAsO${}_{0.9}$F${}_{0.1}$ using Point Contact Andreev Reflection
• Penetration depth, lower critical fields, and quasiparticle conductivity in Fe-arsenide superconductors