Dynamics of chiral antiferroelectric liquid crystal materials exhibiting the S-C alpha* phase

The dynamic properties of chiral smectic liquid crystals are studied theoretically by including competing interlayer interactions leading to the smectic C-alpha* phase below the smectic A phase. In the smectic A phase only one doubly degenerate soft mode exists which becomes critical at the transition temperature for the critical wave vector corresponding to the helicoidal modulation extending over only a few smectic layers. In the tilted smectic C-alpha* phase it splits into two modes, i.e. a phase and an amplitude mode.