String defects in freely suspended liquid-crystal films

Line (string) defects at which the molecular orientation changes by 0, {π}/2, or {π} rad are reported in few-layer-thick freely suspended tilted smectic liquid-crystal films. These defects are ubiquitous, appearing in chiral and nonchiral smectic-C, hexatic, and antiferroelectric phases, either forming closed loops or terminating in fractionally charged vortices. The interaction between strings is complex, there being many ways in which they link to form multiarm (3 to 7) ``star'' and ``tree'' textures.