Gap structure in the electron-doped Iron-Arsenide Superconductor Ba(Fe0.92Co0.08)2As2: low-temperature specific heat study

摘要

We report the field and temperature dependence of the low-temperaturespecific heat down to 400 mK and in magnetic fields up to 9 T of theelectron-doped Ba(Fe0.92Co0.08)2As2 superconductor. Using the phonon specificheat obtained from pure BaFe2As2 we find the normal state Sommerfeldcoefficient to be 18 mJ/mol.K^2 and a condensation energy of 1.27 J/mol. Thetemperature dependence of the electronic specific heat clearly indicate thepresence of the low-energy excitations in the system. The magnetic fieldvariation of field-induced specific heat cannot be described by single clean s-or d-wave models. Rather, the data require an anisotropic gap scenario whichmay or may not have nodes. We discuss the implications of these results.