Charge disproportionation and dynamics in $\theta$-(BEDT-TTF)$_{2}$CsZn(SCN)$_{4}$
R. Chiba, K. Hiraki, T. Takahashi, H. M. Yamamoto, and T. Nakamura

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

© 2008 The American Physical Society.