Abstract
An extensive calorimetric study of the normal- and superconducting-state properties of Ba(Fe1−xCox)2As2 is presented for 0<x<0.2. The normal-state Sommerfeld coefficient increases (decreases) with Co doping for x<0.06 (x>0.06), which illustrates the strong competition between magnetism and superconductivity to monopolize the Fermi surface in the underdoped region and the filling of the hole bands for overdoped Ba(Fe1−xCox)2As2. All superconducting samples exhibit a residual electronic density of states of unknown origin in the zero-temperature limit, which is minimal at optimal doping but increases to the normal-state value in the strongly under- and over-doped regions. The remaining specific heat in the superconducting state is well described using a two-band model with isotropic s-wave superconducting gaps.