Soft mode dynamics in ferroelectric liquid crystals

Abstract

Meyer and coworkers1 have recently discovered ferroelectricity in smectic C and smectic H type liquid crystals. The system observed was p-decyloxybenzylidene p'-amino 2-methyl butyl cinnamate (DOBAMBC). Though the spontaneous polarization is only a fraction of a Debye per molecule and thus much smaller than in crystalline ferroelectrics, the combination of ferroelectricity with liquid-like properties leads to some remarkable effects-flow induced polarization, etc. and makes this new class of ferroelectric materials worthwhile investigating. Another interesting aspect of liquid crystalline ferroelectrics is that-in contrast to solid ferroelectrics-a continuous symmetry group is broken at Tc. The symmetry recovering Goldstone mode thus has below Tc zero excitation energy in the long wavelength limit. This is analogous to isotropic Heisenberg ferromagnets, but quite different from crystalline ferroelectrics where a discrete symmetry is broken at Tc.