Abstract
Many ferroelectric nematic liquid crystals, like one of the archetype materials, DIO, do not have a direct paraelectric N to ferroelectric N(F) phase transition, but exhibit yet another phase between N and N(F). This phase has recently been proposed to be antiferroelectric, with a layered structure of alternating polarization normal to the average director and is sometimes referred to as Smectic Z(A) (SmZ(A)). We have examined the SmZ(A) phase in circularly rubbed (CR) cells, known to discriminate between the polar N(F) and the non-polar N phase from the configuration of disclination lines formed. We find that the ground state of SmZ(A) has the same disclination configuration as the non-polar N phase, demonstrating that the SmZ(A) phase is also non-polar, i.e., it has no net ferroelectric polarization. At the same time, the SmZ(A) texture generally has a grainy appearance, which we suggest is partly a result of the frustration related to layered order combined with the imposed twist in CR cells. We discuss possible orientations of the smectic layers, depending on the alignment conditions. While a horizontal SmZ(A) layer structure is always compatible with surface-induced twist, a vertical layer structure would tend to break up in a twisted bookshelf structure to match non-parallel alignment directions at the two surfaces.