Abstract
We present low-temperature specific heat of the electron-doped Ba(Fe0.9Co0.1)2As2, which does not show any indication of an upturn down to 400 mK, the lowest measuring temperature. The lack of a Schottky-like feature at low temperatures or in magnetic fields up to 9 T enables us to identify enhanced low-temperature quasiparticle excitations and to study anisotropy in the linear term of the specific heat. Our results cannot be explained by a single or multiple isotropic superconducting gap, but are consistent with multi-gap superconductivity with nodes on at least one Fermi surface sheet.
Highlights
Since the discovery of the iron-based pnictide superconductors, substantial experimental and theoretical work has been performed to understand the superconducting (SC) mechanism and its manifestation via the gap structure. [1] Despite these efforts, the gap symmetry is still unclear
In RFeAsO (R: rare earth), the ’1111’ phase, a full gap is expected from Andreev spectroscopy, [2] but a nodal gap is reported from optical measurements [3] for a compound with similar stoichiometry
Conflicting interpretations of the SC order parameter have been reported in Co-doped BaFe2As2 (Ba122 phase)
Summary
Since the discovery of the iron-based pnictide superconductors, substantial experimental and theoretical work has been performed to understand the superconducting (SC) mechanism and its manifestation via the gap structure. [1] Despite these efforts, the gap symmetry is still unclear. Note that, when the nodal behavior is weak (r = 0.55, nodes close to each other), the numerical result using the scattering rates required to explain the residual linear term in the superconducting state exhibits a downturn at low temperatures, not observed experimentally.
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