Sign reversals in the dielectric anisotropy as functions of temperature and frequency in SmA* phase

The authors observe the sign reversals in the dielectric anisotropy as functions of temperature and of frequency in Sm A* phase, for the first time. The sign reversal in the dielectric anisotropy with frequency arises from the molecular relaxation process (fluctuations around the short axis), the same mechanism as for the dual frequency nematics. On the contrary, the sign reversal with temperature is due to the soft mode, which is a dominant collective relaxation process in Sm A* phase and increases ⊥′ sharply with decreasing temperature as the soft mode becomes more dominant close to the Sm CA* to Sm A* transition temperature. We find that the alignment of the cell can be controlled by applying fields of appropriate frequencies at certain temperatures. This method is so effective that we can obtain a homeotropic aligned cell that had previously been planarily aligned by applying an external alternating electric field.