Soliton walls paired by polar surface interactions in a ferroelectric nematic liquid crystal

Surface interactions are responsible for many properties of condensed matter, ranging from crystal faceting to the kinetics of phase transitions. Usually, these interactions are polar along the normal to the interface and apolar within the interface. Here we demonstrate that polar in-plane surface interactions of a ferroelectric nematic N F produce polar monodomains in micron-thin planar cells and stripes of an alternating electric polarization, separated by 180^o domain walls, in thicker slabs. The surface polarity binds together pairs of these walls, yielding a total polarization rotation by 360^o . The polar contribution to the total surface anchoring strength is on the order of 10