Hexatic Order and Herring-Bone Packing in Liquid Crystals

Abstract
A model is proposed for coupled bond-orientational and herring-bone packing degrees of freedom in layered liquid crystals. Three distinct phases are possible: isotropic, and bond-orientationally ordered stacked hexatic with and without herring-bone order. The transition between the two ordered phases is first order. The isotropic-hexatic transition can be driven first order by fluctuations and becomes second order at a tricritical point. Available experimental data are consistent with our model.