COVARIANT ELASTICITY AND DISLOCATIONS IN SMECTIC-C LIQUID-CRYSTALS

We derive a rotationally invariant form for the elastic energy of a sm ectic-C liquid crystal. The magnitude of the c director, but not its d irection, can screen layer strain just as two independent components o f the director screen strain in smectic-A liquid crystals. Type I and type II smectic-C liquid crystals can be classified according to wheth er the c-director penetration depth lambda(c) is less than or greater than the smectic coherence length xi. We calculate the energies of iso lated dislocations and the interaction energies of parallel dislocatio ns as a function of direction. We find an attractive interaction at la rge distances between like-sign screw dislocations and a repulsive int eraction at short distances, leading to a minimum energy separation.