title: Specific heat measurements of Ba(0.68)K(0.32)Fe2As2 single crystals: evidence for a multiband strong-coupling superconducting state.
abstract: The specific heat of high-purity Ba(0.68)K(0.32)Fe2As2 single crystals with the highest reported superconducting Tc=38.5 K was studied. The electronic specific heat Cp below Tc shows two gap features, with Δ1≈11 meV and Δ2≈3.5 meV obtained from an α-model analysis. The reduced gap value, 2Δ(max)/kBTc≈6.6, the magnitude of the specific-heat jump, ΔCp(Tc)/Tc, and its slope below Tc exhibit a strong-coupling character. We also show that an Eliashberg model with two hole and two electron bands gives the correct values of Tc, the superconducting gaps, and the free-energy difference.
authors.affiliation: Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Popovich
authors.forename: A V
authors.initials: AV
authors.lastname: Boris
authors.forename: O V
authors.initials: OV
authors.lastname: Dolgov
authors.forename: A A
authors.initials: AA
authors.lastname: Golubov
authors.forename: D L
authors.initials: DL
authors.lastname: Sun
authors.forename: C T
authors.initials: CT
authors.lastname: Lin
authors.forename: R K
authors.initials: RK
authors.lastname: Kremer
authors.forename: B
authors.initials: B
authors.lastname: Keimer