The order parameter and the Landau expansion in the chiral smectic C phase

Abstract

Different order parameters have been proposed by various authors for the description of the smectic C phase and for the phase transition smectic A to smectic C. How the choice of order parameters is made is of importance for the Landau expansion of the free energy, and could also have importance for the range of applicability of this expansion. A parameter characterizing the hindered rotation around the long axis is suggested as a suitable secondary order parameter, replacing the spontaneous polarization in this role. The contribution to the specific heat from such hindered rotation is compared with experimental values. A tensorial order parameter is introduced, and this gives implications for the ordinary Landau expansion in terms of the tilt angle.