LANDAU-DE GENNES THEORY OF THE CORE STRUCTURE OF A SCREW DISLOCATION IN SMECTIC-A LIQUID-CRYSTALS

We present details of calculations of the core structure of a screw di slocation in a smectic A liquid crystal, using the phenomenological La ndau-de Gennes free energy functional. The order parameter frustration created by topological constraints far from the dislocation core is r esolved in one of three qualitatively different ways. The three types of dislocation core solution are the DT (double twist), CL (classical) , and BP (broken polar symmetry) solutions, respectively. The stabilit y requirements for these structures are discussed, as a function of te mperature, smectic elastic properties, and coupling between smectic an d nematic order. The effect of possible inhomogeneity between left- an d right-handed conformers is also examined.