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The specific heat down to 0.08 K of the iron pnictide superconductor KFe2As2was 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 fieldnormal state specific heat divided by temperature, C/T, was extrapolated fromabove Tc to T=0 by insisting on agreement between the extrapolated normal stateentropy 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 beequal. This extrapolation would indicate that this rather clean sample ofKFe2As2 exhibits non-Fermi liquid behavior, i. e. C/T increases at lowtemperatures, in agreement with the reported non-Fermi liquid behavior in theresistivity. However, specific heat as a function of magnetic field shows thatthe shoulder feature around 0.7 K, which is commonly seen in KFe2As2 samples,is not evidence for a second superconducting gap as has been previouslyproposed but instead is due to an unknown magnetic impurity phase, which canaffect the entropy balance and the extrapolation of the normal state specificheat. This peak (somewhat larger in magnitude) with similar field dependence isalso found in a less pure sample of KFe2As2, with a residual resistivity ratioof only 90 and an onset Tc=3.1 K. These data, combined with the measured normalstate specific heat in field to suppress superconductivity, allow theconclusion that an increase in the normal state specific heat as T->0 is infact not seen in KFe2As2, i. e. Fermi liquid behavior is observed.

Specific heat in KFe2As2 in zero and applied magnetic field