We report on specific-heat measurements in ${\text{Ba}}_{1-x}{\text{K}}_x{\text{Fe}}_2{\text{As}}_2$ $\left(x\le 0.6\right)$. For the underdoped sample with $x=0.2$, both the spin-density-wave transition at $T=100\text{K}$ and the superconducting transition at 23 K can be identified. After subtraction of the normal-state specific heat by appropriate Debye and Einstein contributions and the normal-state Sommerfeld coefficient, we can describe the electronic contribution to the specific heat in the superconducting state for concentrations $0.3\le x\le 0.6$ by a full single gap within the BCS limit.

• Received 2 October 2009

DOI:https://doi.org/10.1103/PhysRevB.81.014529