131 research outputs found

    Effect of annealing on the specific heat of optimally doped Ba(Fe0.92_{0.92}Co0.08_{0.08})2_{2}As2_{2}

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    We report the temperature dependence of the low-temperature specific heat down to 400 mK of the electron-doped Ba(Fe0.92_{0.92}Co0.08_{0.08})2_{2}As2_{2} superconductors. We have measured two samples extracted from the same batch: first sample has been measured just after preparation with no additional heat treatment. The sample shows TcT_{c}=20 K, residual specific heat Ξ³0\gamma_{0}=3.6 mJ/mol K2^{2} and a Schottky-like contribution at low temperatures. A second sample has been annealed at 800 oC^{o}C for two weeks and shows TcT_{c} = 25 K and Ξ³0\gamma_{0}=1.4 mJ/mol~K2^{2}. By subtracting the lattice specific heat, from pure BaFe2_{2}As2_{2}, the temperature dependence of the electronic specific heat has been obtained and studied. For both samples the temperature dependence of Cel(T)C_{el}(T) clearly indicate the presence of low-energy excitations in the system. Their specific heat data cannot be described by single clean s- or d-wave models and the data requires an anisotropic gap scenario which may or may not have nodesComment: SCES 2010, 5 pages, 2 figure

    Calorimetric Evidence for Nodes in the Overdoped Ba(Fe0.9_{0.9}Co0.1_{0.1})2_{2}As2_{2}

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    We present low-temperature specific heat of the electron-doped Ba(Fe0.9_{0.9}Co0.1_{0.1})2_{2}As2_{2}, 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 Tesla enables us to identify enhanced low-temperature quasiparticle excitations and to study anisotropy in the linear term of the specific heat. Our results can not 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.Comment: 5 pages 4 figure
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