Evidence for dynamic spin fluctuation in specific heat of Sr$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ crystals

We measured the zero-field specific heat in Sr$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ system. The sommerfeld coefficients $\gamma$ contracting to the band-structure predict, shows a four-fold jump between the non-superconductive SrFe$_{2}$As$_{2}$ and the optimally doped Sr$_{0.55}$K$_{0.45}$Fe$_{2}$As$_{2}$. We also found that the electronic contribution actually change significantly with temperature, and cannot be attributed to the entropy of the static spin-density-wave (SDW) alone. Together with its unusual doping dependency, the data suggest the existence of dynamic spin fluctuations. The residual electronic specific heat further suggests a possible phase-separation in the region where SC (superconductivity) and SDW coexist.