Dielectric response in the charge-ordered θ-(BEDT-TTF)2RbZn(SCN)4 organic compound

We report measurements of low-frequency dielectric permittivity in two-dimensional theta-(BEDT-TTF)(2)RbZn(SCN)(4) organic compound. The real part of the dielectric permittivity epsilon' exhibits a sharp peak in the extreme vicinity of the charge ordered phase transition at T-CO. The very low magnitude of epsilon' below T-CO results from the lattice dimerization asssociated with the charge ordered phase. We ascribe the temperature-dependent permittivity above T-CO to pre-existing charge inhomogeneities-charge disproportionation-as revealed previously by NMR measurements. A qualitative comparison between the dielectric response due to charge order in quasi-one-dimensional conductors and in this two-dimensional system is presented.