Uncovering Collective Modes Underlying the Giant Dielectric Response of Ferroelectric Nematic Liquid Crystals

Abstract

Ferroelectric nematic liquid crystals (FNLCs) are polar fluids in which spontaneous polarization coexists with nematic orientational order, giving rise to unusual dielectric and electromechanical responses. However, the collective modes underlying their giant dielectric response remain unclear. Here, we show that this response originates from the superposition of two distinct relaxation modes rather than a single process. Dielectric spectroscopy reveals that the low-frequency mode exhibits soft-mode-like behavior associated with short-axis molecular rotation, whereas the high-frequency mode corresponds to a Goldstone-like phase displacement of an effective transverse polarization component rotating around the director. These assignments are supported by systematic analyses of temperature, electric-field, cell-thickness, and alignment-layer dependences. Our results demonstrate that the giant dielectric response of ferroelectric nematics reflects multiple collective polarization dynamics with different symmetries and restoring forces, providing a framework for interpreting dielectric spectra in polar nematic fluids.