Electronic ground state of θ-(BEDT-TTF)2RbZn(SCN)4studied by Raman spectroscopy

Polarized Raman spectra were measured to study the charge distribution in the insulating phase of θ-(BEDT-TTF) 2 RbZn(SCN) 4 . The Raman spectra exhibited complicated multiplet pattern around the C=C stretching region, though the donor molecule has only two symmetric normal modes associated to the C=C bonds. Emergence of the multiple peaks implied the substantial charge disproportionation. We investigated the spatial symmetry of the charge distribution by measuring the polarization dependence of the Raman signals and the infrared reflectance spectra by taking into account charge imbalance dividing the tetramer into two pairs of molecules.