Zusammenfassung
The two-dimensional organic charge-transfer salt κ -(BEDT-TTF) 2 CuN(CN) 2 -Br x Cl 1– x is tuned across the metal-insulator transition by varying the Br content. Temperature dependent measurements of the optical conductivity yield information on the electrodynamics of the half-filled correlated electron system. At room temperature a broad incoherent response is observed with no clear Drude peak. As the temperature drops below 50 K, an energy gap develops in the Cl-rich samples which grows to approximately 1000 cm −1 for T → 0. With increasing Br concentration spectral weight shifts into the gap region and eventually fills it up completely. A Drude-like component develops due to the coherent quasiparticles.
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