We report on specific heat measurements in Ba$_{ 1-x}$K$_x$Fe$_{ 2}$As$_{ 2}$ ($x\le 0.6$). For the underdoped sample with $x=0.2$ both the spin-density-wave transition at $T = 100$ K and the superconducting transition at 23 K can be identified. The electronic contribution to the specific heat in the superconducting state for concentrations in the vicinity of optimal doping $x=0.4$ can be well described by a full single-gap within the BCS limit.
Categories: cond-mat.supr-con