Observation of Ferroelectricity in a Thermotropic Nematic Liquid Crystal Using its Spectacular Electro-Optics*

We have synthesized and studied the literature compound RM734 [1], a polar rod shaped molecule exhibiting a typical nematic phase and a second nematic phase assigned to be a "splay nematic" state [2]. We find that the second phase is rather a thermotropic ferroelectric nematic, an identification based on the first observation in a nematic of the defining characteristics of ferroelectricity: (1) the formation, in absence of applied electric field, of spontaneously polar domains of opposite sign of polarization separated by distinct domain boundaries; and (2) field-induced polarization reversal mediated by movement of these domain boundaries. A truly remarkable feature of this phase is the magnitude of its spontaneous polarization, saturating at 6 μC/cm², the largest ever reported for an organic material or for any fluid, and larger than that of all but a few crystalline ferroelectrics.

Works Cited

[1] Mandle RJ,et al. (2017). Rational Design of Rod-Like Liquid Crystals Exhibiting Two Nematic Phases. Chemistry - A European Journal, 23 14554-14562.
[2] Mertelj, A. et al. (2018). Splay Nematic Phase. Phys. Rev. X, 8, 041025.