  The dielectric constant and ac conductivity have been measured for the
layered organic conductor theta-(BEDT-TTF)_2CsZn(SCN)_4 along the out-of-plane
direction, which show a relaxation behavior similar to those in the
charge-density-wave conductor. Most unexpectedly, they exhibit a large bias
dependence with a hysteresis, and changes in magnitude by 100-1000 times at a
threshold. These findings are very similar to the collective excitation of the
charge density wave. theta-$(BEDT-TTF)_2CsZn(SCN)_4 has collective excitations
associated with charge ordering, though it shows no clear indication of long
range order.
