  An axial next-nearest-neighbor XY model is studied as a model of chiral
liquid crystals which exhibit many ferro-, ferri- and antiferroelectric tilted
smectic phases. Depending on the values of interaction parameters, this model
exhibits Ising symmetric (i.e., the tilt directions of directors are parallel
or anti parallel) phases or XY symmetric phases. Phases with each
type-of-symmetry show the character of devil's staircase, which has been
observed in experiments.
