FRONT PROPAGATION INTO UNSTABLE AND METASTABLE STATES IN SMECTIC-C-ASTERISK LIQUID-CRYSTALS - LINEAR AND NONLINEAR MARGINAL-STABILITY ANALYSIS

We discuss the front propagation in ferroelectric chiral smectic liquid crystals (Sm-C*) subjected to electric: and magnetic fields that are applied parallel to smectic layers. The reversal of the electric field induces the motion of domain walls or fronts that propagate into either an unstable or a metastable state. In both regimes,the front velocity is calculated exactly. Depending on the field, the speed of a front propagating into the unstable state is given either by the so-called linear marginal-stability velocity of by the nonlinear marginal-stability expression. The crossover between these two regimes can be tuned by a magnetic field. The influence of initial conditions on the velocity selection problem can also be studied in such experiments. Sm-C* therefore offers a unique opportunity to study different aspects of front propagation in an experimental system.