3A09 反強誘電性液晶における方位角分布と逐次相転移

抄録

The phase transitions of axial next nearest neighbour XY model (ANNNXY model) with biquadratic interaction is studies to elucidate the crossover from XY model to Ising model, in relation to the behaviour of the direction of the molecular tilt in the phenomena of successive phase transitions of antiferroelectric smectics. At the ground state, the freedom of the XY spin is easily suppressed, while at finite temperature the phase with XY symmetry appears near the critical temperature in the wide range of strength of the biquadratic interaction. The change from the Ising symmetry to the XY one occurs discontinuously, which differs from the crossover behaviour occurring at the similar system with 2-fold field in place of the biquadratic interaction where the crossover occurs continuously.