The effect of biasing electric field on relaxations in FLC investigated by the dielectric and optical methods

Abstract

The dielectric and electrooptical responses within the frequency range 30 Hz–100 kHz are used to study the properties of the soft and the Goldstone mode in dependence of bias electric field. It is shown that the soft mode relaxation frequency is linearly bias dependent in both SmA and SmC* phases, the Goldstone mode relaxation frequency is constant for small bias. After the modulated structure is unwound a low frequency mode persists a relaxation frequency of which also linearly increases with increasing bias. This mode is connected with vibration of molecules around the layer normal keeping the constant tilt angle, which could take place in surface layers. The Cole—Cole diagrams constructed from the optical response are obtained for all studied modes in the shape of semicircles, showing all the modes have relaxation character with well defined relaxation frequencies. The bias field dependencies of both optical and dielectric responses in the SmC* phase reflect the unwinding process of the helicoidal and twisted structure.