Evolution of Superconducting Gaps in Th-Substituted Sm${}_{1-x}$Th${}_x$OFeAs Studied by Multiple Andreev Reflection Spectroscopy

Abstract

Using intrinsic multiple Andreev reflections effect (IMARE) spectroscopy, we studied SnS contacts in the layered oxypnictide superconductors Sm${}_{1-x}$Th${}_x$OFeAs with various thorium doping and critical temperatures $T_C=21-54$ K. We observe a scaling between both superconducting gaps and $T_C$. The determined BCS-ratio for the large gap $2{\Delta }_L/k_B{T}_C=5.0-5.7$ and its eigen BCS-ratio (in a hypothetical case of zero interband coupling) $2{\Delta }_L/k_B{T}_C^L=4.1-4.6$ both exceeding the weak-coupling limit 3.52, and for the small gap $2{\Delta }_S/k_B{T}_C=1.2-1.6$ remain nearly constant within all the $T_C$ range studied. The temperature dependences ${\Delta }_{L,S}(T)$ agree well with a two-band BCS-like Moskalenko and Suhl model. We prove intraband coupling to be stronger than interband coupling, whereas and Coulomb repulsion constants ${\mu }^{\ast }$ are finite in Sm-based oxypnictides.

12 pages, 14 figures

References in corpus (13)

• The BCS-like gap in superconductor SmFeAsO_0.85F_0.15
• Superfluid density and specific heat within self-consistent scheme for two-band superconductor
• Electronic Structure of Fe-Based Superconductors
• Magnetic penetration depth of single crystal SmFeAsO_{1-x}F_y: a fully gapped superconducting state
• Scanning tunneling spectroscopy of SmFeAsO0.85: Possible evidence for d-wave order parameter symmetry
• High-pressure flux growth, structural, and superconducting properties of LnFeAsO (Ln = Pr, Nd, Sm) single crystals
• Nodal Superconductivity with Multiple Gaps in SmFeAsO${}_{0.9}$F${}_{0.1}$
• Possible two-gap superconductivity in NdFeAs(O,F) probed by point-contact Andreev-reflection spectroscopy
• Th substituted SmFeAsO: structural details and superconductivity with Tc above 50 K
• Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor
• Unexpected impact of magnetic disorder on multiband superconductivity
• Effects of isoelectronic Ru substitution at the Fe site on the energy gaps of optimally F-doped SmFeAsO
• Direct observation of ballistic Andreev reflection

Cited by in corpus (1)

• Signature of multigap nodeless superconductivity in fluorine-doped NdFeAsO