Tunable defect patterns induced by a low-frequency electric field in ferroelectric nematic liquid crystals

The regulation of topological structures and pattern formation has attracted wide attention in the field of condensed matter. Liquid crystals (LCs), as a class of soft matter, uniquely combine fluidity with anisotropic properties, making them ideal systems for exploring defect dynamics. When confined systems are subjected to external stimuli, LCs can exhibit a variety of topological defects. The recent discovery of ferroelectric nematics (N_F), characterized by high permittivity and spontaneous polarization, has opened new possibilities for technological applications, enriching the landscape of accessible topological phenomena. In this study, we demonstrate the formation of tunable two-dimensional arrays of topological defects in an N_F compound, induced by an alternating electric field in sandwich cells without pre-patterning. These defects self-organize into pseudo-square lattices, with their character and periodicity governed primarily by the frequency of the applied field and, to a lesser extent, by the cell thickness. We attribute the emergence of these structures to the interplay between elastic and electric forces appearing as a result of polar molecular reorientation. Our findings offer a promising approach for generating reconfigurable, spatially periodic polarization patterns, with potential relevance to future soft-matter-based devices and tunable photonic systems.