Phase transitions and solitons in liquid crystals

Abstract Phase transitions occurring in liquid crystals are reviewed from a viewpoint of solitons. First, cholesteric-nematic phase transition is explained as a condensation process of solitons. This mechanism of phase transition is common to the so-called commensurate-incommensurate phase transition. In the next place, not only liquid crystals such as chiral smectic C and smectic A phases but also ferroelectrics and some other systems belonging to this category and its generalized versions arc introduced, and discussed especially in relation to an order of phase transition, where a symmetry of periodic phases on an order parameter space gives the basis of the consideration.