  The specific heat down to 0.08 K of the iron pnictide superconductor KFe2As2
was measured on a single crystal sample with a residual resistivity ratio of
~650, with an onset Tc determined by specific heat of 3.7 K. The zero field
normal state specific heat divided by temperature, C/T, was extrapolated from
above Tc to T=0 by insisting on agreement between the extrapolated normal state
entropy at Tc, Sn(Tc), and the measured superconducting state entropy at Tc,
Ss(Tc), since for a second order phase transition the two entropies must be
equal. This extrapolation would indicate that this rather clean sample of
KFe2As2 exhibits non-Fermi liquid behavior, i. e. C/T increases at low
temperatures, in agreement with the reported non-Fermi liquid behavior in the
resistivity. However, specific heat as a function of magnetic field shows that
the shoulder feature around 0.7 K, which is commonly seen in KFe2As2 samples,
is not evidence for a second superconducting gap as has been previously
proposed but instead is due to an unknown magnetic impurity phase, which can
affect the entropy balance and the extrapolation of the normal state specific
heat. This peak (somewhat larger in magnitude) with similar field dependence is
also found in a less pure sample of KFe2As2, with a residual resistivity ratio
of only 90 and an onset Tc=3.1 K. These data, combined with the measured normal
state specific heat in field to suppress superconductivity, allow the
conclusion that an increase in the normal state specific heat as T->0 is in
fact not seen in KFe2As2, i. e. Fermi liquid behavior is observed.
