Charge disproportionation and dynamics in θ-(BEDT-TTF)2CsZn(SCN)4

The electronic state of two-dimensional organic conductor, theta-(BEDT-TTF)(2)CsZn(SCN)4, has been investigated by means of C-13-NMR line shape analyses on selectively C-13-enriched single crystal sample. Strong charge disproportionation was found to develop in the metallic state well above metal-insulator transition temperature of similar to 20 K. The charge disproportionation becomes almost static below similar to 140 K, forming a shor-trange charge ordering, but no long-range ordering is stabilized at low temperatures down to 5 K. About half of the molecular sites become nonmagnetic, while the other half carries finite magnetic moments. Charge disproportionation becomes very much reduced at least at the nonmagnetic molecular sites, implying that charge rearrangement occurs at similar to 20 K.