Bandwidth-controlled Mott transition in κ-(BEDT-TTF)₂ Cu [N(CN)₂] Brₓ Cl₁₋ₓ I. Optical studies of localized charge excitations

الأصل · EN

Infrared reflection measurements of the half-filled two-dimensional organic conductors κ-(BEDT-TTF)₂Cu[N(CN)₂]BrₓCl₁₋ₓ were performed as a function of temperature (5 K<T<300 K) and Br-substitution (x=0%, 40%, 73%, 85%, and 90%) in order to study the metal-insulator transition. We can distinguish absorption processes due to itinerant and localized charge carriers. The broad mid-infrared absorption has two contributions: transitions between the two Hubbard bands and intradimer excitations from the charges localized on the (BEDT-TTF)₂ dimer. Since the latter couple to intramolecular vibrations of BEDT-TTF, the analysis of both electronic and vibrational features provides a tool to disentangle these contributions and to follow their temperature and electronic-correlations dependence. Calculations based on the cluster model support our interpretation.