Head-tail asymmetry of a molecule as a microscopic origin of the successive phase transitions in chiral smectics

The head-tail asymmetry is distinction between energy of a pair of rod-like molecules in head-to-head configuration and energy of the pair in tail-to-tail or head-to-tail configuration. We use a molecular model system to consider a role of the head-tail asymmetry for the phase transitions of chiral smectics. Mean field theory indicates that our model system shows the existence of various types of intermediate phases such as Sm-C-gamma* and AF phase between antiferroelectric Sm-C-A* phase and ferroelectric Sm-C* phase. One of origins of the existence of the intermediate phases is the ordering of heads which induce interactions between separated smectic layers.