Revealing the antipolar order in the antiferroelectric SmZA phase by means of circular alignment

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.