Abstract and subjects
We report the temperature dependence of the low-temperature specific heat down to 400 mK of the electron-doped Ba(Fe0.92Co (0.0 8))(2)As-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 T-c=20 K, residual specific heat gamma(0)=3.6 mJ/mol K-2 and a Schottky-like contribution at low temperatures. A second sample has been annealed at 800 degrees C for two weeks and shows T-c=25 K and gamma(0)=1.4 mJ/mol K-2. By subtracting the lattice specific heat, from pure BaFe2As2, the temperature dependence of the electronic specific heat has been obtained and studied. For both samples the temperature dependence of 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 nodes.