Imperfect defects in smectics A

Abstract

In real samples, focal conic domains (FCDs) and double helical domains (DHDs) in smectic A phases are frequently distorted. Distortions show up as imperfections of conjugated disclinations. These are induced imperfections in difference with proper imperfections, which in terms of the extended Volterra process are inevitable structural features of any curved disclination, including conjugated disclinations of an ideal FCD and DHD. The paper reviews experimental observations of induced imperfections of disclinations in FCDs and DHDs in non-chiral and chiral smectic A and A* phases. Imperfections of FCDs and DHDs are documented as giant kinks on their disclinations or due to the deviation of the shapes of disclinations from those geometrically predicted for conjugated conics. The main message of this paper is that the induced imperfections of FCDs and DHDs are due to the interaction of disclinations with dislocations. The interaction of disclinations with dislocations is suggested to be the driving mechanism for the temperature evolution of FCDs in nematogenic SmA as well as DHDs* in chiral SmA* phases under the temperature variation and applied electric field.