Discrete Soliton with Variable Amplitude in Electric Field Induced SmC_α*-SmC Transition

Abstract

A helix of chiral smectic C α phase (SmC α * ) is unwound by an electric field and a transition to smectic C phase (SmC) occurs at a certain field strength. The phenomenon is interpreted as a discrete soliton condensation, which is compared with a transition from chiral smectic C phase (SmC * ) to SmC driven by the electric field where a mechanism of the transition has been analyzed as a condensation of sine-Gordon soliton. Under the condition of constant tilt angle of molecular long axis at SmC α * , the transition is known to be continuous and eventually an interaction between solitons is repulsive so long as a pitch of the helix without the field is larger than four smectic layers. Here, effects due to variable tilt on the transition and the interaction between discrete solitons are studied. At low temperature region where the tilt angle is large enough, the transition remains continuous, which is similar to the behaviour at the constant tilt. On the other hand at high temperature adjacent to the transition between SmC α * and smectic A phase, the transition changes to a discontinuous one and the interaction between discrete solitons turns to attractive one. Behaviour of soliton tail is compared with the order of the transition, that is, in a region of the continuous transition the tail decays exponentially, while in the discontinuous transition region the tail decays oscillatory.