Mean-Field Theory of the Uniaxial Ferroelectric Smectic A Liquid Crystal Phase.

Following the groundbreaking discovery of the ferroelectric nematic liquid crystal phase (N_{F}), a series of closely-related new polar phases have also been found. An especially interesting one is the ferroelectric smectic A phase (SmA_{F}) with spontaneous polarization along the layer normal observed in a few materials of the N_{F} realm. Here, we present a mean-field molecular model that successfully captures the rich phase diagrams experimentally observed in the literature in terms of two parameters. Additionally, we carry out second harmonic generation, X-ray diffraction, and birefringence measurements in a compound exhibiting the SmA_{F} phase to determine the appropriate order parameters and compare with the model predictions.