Incoherent Interplane Response of FeTe$_{0.55}$Se$_{0.45}$

We investigated the interplane $c$ axis electronic response of iron-chalcogenide superconductor FeTe$_{0.55}$Se$_{0.45}$ using infrared spectroscopy. We found that the normal-state $c$ axis electronic response of FeTe$_{0.55}$Se$_{0.45}$ is incoherent. The $c$ axis optical conductivity does not display well-defined Drude response and it becomes further suppressed with decreasing temperature. This normal-state $c$ axis optical response is remarkably similar to that of the mildly underdoped cuprates but is in sharp contrast to the coherent $c$ axis response of Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$. From the analyses on the electronic anisotropy of various layered superconductors, we found a close correlation between the degree of the coherence in the $c$ axis transport and the strength of the dissipation in the \textit{ab} plane response.