Pretransitional Behavior of Birefringence in a Smectic-BLiquid Crystal near the Smectic-APhase

The birefringence has been measured in detail near the smectic-$A$ to smectic-$B$ phase transition in N-($p$-butoxybenzylidene)-$p$-$n$-octylaniline. The birefringence undergoes a sharp discontinuity of 2.5×${10}^{-3\mathrm{}}$ within 2 mK at the transition. A pretransitional behavior in both the birefringence and the response time is found in a temperature interval of 0.3 K below the transition. The change in birefringence in the smectic-$B$ phase follows a parabolic temperature dependence.