Electron-Molecular Vibrational Coupling and Electronic Structure of κ-(BEDT-TTF)2Cu[N(CN)2]Cl0.5Br0.5: Optical Study at Temperatures Down to 15 K.

Electron-molecular vibration (EMV) coupling in organic solids attracts considerable attention because of various interesting and important effects, including a possible origin of superconductivity in these materials [1]. Infrared spectroscopy presents a convenient way to study the EMV coupling in the low-dimensional solids [2, 3]. In this paper, we present the polarized infrared spectroscopic study of single crystals of κ-(ET)2Cu[N(CN)2]Cl0.5Br0.5 (superconductor at ambient pressure below 11.3 K) in a wide temperature range down to 15 K and the theoretical description of their optical properties based on the “phase phonon” theory [4] and the cluster model [5]. The results of the reflectance spectra studies for (ET)2Cu[N(CN)2]Cl0.5Br0.5 at room temperature have been reported earlier [6].