双轴诱导近晶A-C三临界点附近的近晶De Vries行为
De Vries Behavior in Smectics near a Biaxiality Induced Smectic A - Smectic C Tricritical Point
摘要：
我们表明，广义朗道理论的近晶A和C阶段表现出双轴诱导AC三临界点。接近这个三临界点取决于系统中取向顺序的程度;对于足够大的取向顺序，AC转变是3D XY样的，而对于足够小的取向顺序，它是三临界或1阶。我们调查的三种类型的AC过渡附近的三临界性，并表明，对于每一种类型的过渡，小取向顺序意味着德弗里斯行为的层间距，一个异常小的层收缩。这一结果与de Vries的“扩散锥”模型一致，并且可以用该模型来理解。此外，我们表明，双折射增长后进入C相。对于连续过渡，过渡越接近三临界，这种增长就越快。我们的模型还预测了双折射的非单调温度依赖性的可能性。
英文摘要：
We show that a generalized Landau theory for the smectic A and C phases exhibits a biaxiality induced AC tricritical point. Proximity to this tricritical point depends on the degree of orientational order in the system; for sufficiently large orientational order the AC transition is 3D XY-like, while for sufficiently small orientational order, it is either tricritical or 1st order. We investigate each of the three types of AC transitions near tricriticality and show that for each type of transition, small orientational order implies de Vries behavior in the layer spacing, an unusually small layer contraction. This result is consistent with, and can be understood in terms of, the "diffuse cone" model of de Vries. Additionally, we show that birefringence grows upon entry to the C phase. For a continuous transition, this growth is more rapid the closer the transition is to tricriticality. Our model also predicts the possibility of a nonmontonic temperature dependence of birefringence.
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