Field-induced SmCa*-SmC transition and the structural change

Abstract

SmCa* and SmC* are ferroelectric and have helical structures, and both phase changes to SmC by an electric field. The transition for SmC* is interpreted as a soliton condensation. In contrast with SmC*, the soliton becomes a discrete type at SmCa* because a pitch is quite short. Here, we study how the transition to SmC occurs in the discretized description and how properties of the soliton accompanied with the transition change. It is shown that the transition to SmC is continuous and interaction between solitons is repulsive though the interaction is very short range. A field-dependence of a wave number makes a devil's staircase, and a free energy curve for the wave number is non-differentiable at any rational wave number. These properties are in contrast with those at the continuous description where both curves are analytic. Experimental facts on the apparent optical axis and polarization current are compared with the present results.