Comment on "Mechanism of Terahertz Electromagnetic Wave Emission from Intrinsic Josephson Junctions"

In a recent Letter, Tachiki \emph{et al.} argued that the dynamic state of superconductivity phase in multi junctions characterized by $\pm\pi$ kinks is hard to realize from an energetic point of view. Instead, they proposed a so-called "state without kink". In this Comment, we point out that their energetic consideration is inconsistent with the well established treatment for Josephson junctions, and that the results derived for their "state without kink" cannot explain the radiations observed in the recent experiment.