Collapse of coherent quasiparticle states in θ-(BEDT-TTF)2I3 observed by optical spectroscopy -: art. no. 227801

Optical conductivity measurements on the organic metal theta-(BEDT-TTF)(2)I-3 revealed that the system crosses over rapidly from a coherent quasiparticle state to an incoherent state with temperature. Despite the metallic temperature dependence of resistivity, a well-defined Drude peak at low temperatures turns into a far-infrared peak with temperature. The peak energy shifts to higher frequencies and, simultaneously, the spectral weight is transferred to high frequencies beyond the electron band width. These characteristics imply that theta-(BEDT-TTF)(2)I-3, so far believed to be a typical metal, is in fact a strongly correlated electron system with bad-metal character.