title: Universal heat conduction in the iron arsenide superconductor KFe2As2: evidence of a d-wave state.
abstract: The thermal conductivity κ of the iron arsenide superconductor KFe2As2 was measured down to 50 mK for a heat current parallel and perpendicular to the tetragonal c axis. A residual linear term at T→0, κ(0)/T is observed for both current directions, confirming the presence of nodes in the superconducting gap. Our value of κ(0)/T in the plane is equal to that reported by Dong et al. [Phys. Rev. Lett. 104, 087005 (2010)] for a sample whose residual resistivity ρ(0) was 10 times larger. This independence of κ(0)/T on impurity scattering is the signature of universal heat transport, a property of superconducting states with symmetry-imposed line nodes. This argues against an s-wave state with accidental nodes. It favors instead a d-wave state, an assignment consistent with five additional properties: the magnitude of the critical scattering rate Γ(c) for suppressing T(c) to zero; the magnitude of κ(0)/T, and its dependence on current direction and on magnetic field; the temperature dependence of κ(T).
authors.affiliation: Département de physique and RQMP, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: J-Ph
authors.initials: JP
authors.lastname: Reid
authors.forename: M A
authors.initials: MA
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authors.lastname: Juneau-Fecteau
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authors.lastname: Gordon
authors.forename: S René
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authors.lastname: de Cotret
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authors.lastname: Doiron-Leyraud
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authors.lastname: Saito
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authors.lastname: Fukazawa
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authors.lastname: Kohori
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authors.lastname: Kihou
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authors.lastname: Iyo
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authors.lastname: Eisaki
authors.forename: R
authors.initials: R
authors.lastname: Prozorov
authors.forename: Louis
authors.initials: L
authors.lastname: Taillefer