Comment on ``Collapse of Coherent Quasiparticle States in θ-(BEDT-TTF)2I3 Observed by Optical Spectroscopy''
Abstract
Recently, Takenaka et al. reported that the resistivity rho(T) of theta-(BEDT-TTF)2I3 (theta-ET) exceeds the Ioffe-Regel resistivity by a factor of 50 at large temperatures T (``bad metal''). This was ascribed to strong correlation. We argue that the optical conductivity sigma(omega) implies that correlation is not very strong, and that correlation gives no general strong suppression of sigma(omega). The large rho(T) is primarily due to a downturn in sigma(omega) at small omega, earlier emphasized by Takenaka et al. as the explanation for bad metal behavior of high-Tc cuprates. We argue, however, that for cuprates strong correlation is the main effect. The data of Takenaka et al. puts theta-ET in a new class of bad metals.
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