The dependence on the helical pitch of the antiferroelectric dielectric modes

In an attempt to determine the physical nature of the low-frequency dielectric mode in antiferroelectric liquid crystals, we have studied the dielectric response in thick planar-oriented samples of Smectic C/sub A/* compounds undergoing a helix inversion. If the mode is collective there ought to be a minimum in the dielectric absorption due to the mode, at the temperature at which the helical pitch diverges. Although the effect is not large, we find minima for both antiferroelectric modes at this point, indicating that both modes are related to the helical director structure. A corresponding experiment has also been performed on a binary mixture which shows a helix inversion for a certain mixing ratio. However, because the effect in this case is overshadowed by unavoidable variations in other parameters, no minimum was detected.