Reflectance Spectra of κ-(BEDT-TTF)2I3:Electronic Structure of Dimeric BEDT-TTF Salts

Polarized reflectance spectra of a single crystal of κ-(BEDT-TTF) 2 I 3 were measured at 295 K and 15 K over the spectral range from 500 cm -1 to 25000 cm -1 . The infrared property was two-dimensional. Non-Drude mid-infrared features were observed in spite of the metallic dc conductivity. A comparison with β- and θ-(BEDT-TTF) 2 I 3 shows that this behavior has a close connection with the dimeric structure of κ-salts. We analyzed the observed line shape by the curve-fitting analysis, and obtained optical effective masses. On the basis of the perturbation theory, an effective tight-binding band model for κ-salt was derived. We estimated the transfer integrals using this model.