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1. The smectic Z _A phase: Antiferroelectric smectic order as a prelude to the ferroelectric nematic

   https://doi.org/10.1073/pnas.2217150120  

   Chen, Xi; Martinez, Vikina; Korblova, Eva; Freychet, Guillaume; Zhernenkov, Mikhail; Glaser, Matthew A.; Wang, Cheng; Zhu, Chenhui; Radzihovsky, Leo; Maclennan, Joseph E.; et al (February 2023, Proceedings of the National Academy of Sciences)

   We have structurally characterized the liquid crystal (LC) phase that can appear as an intermediate state when a dielectric nematic, having polar disorder of its molecular dipoles, transitions to the almost perfectly polar-ordered ferroelectric nematic. This intermediate phase, which fills a 100-y-old void in the taxonomy of smectic LCs and which we term the “smectic Z A ,” is antiferroelectric, with the nematic director and polarization oriented parallel to smectic layer planes, and the polarization alternating in sign from layer to layer with a 180 Å period. A Landau free energy, originally derived from the Ising model of ferromagnetic ordering of spins in the presence of dipole–dipole interactions, and applied to model incommensurate antiferroelectricity in crystals, describes the key features of the nematic–SmZ A –ferroelectric nematic phase sequence. 

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2. Energetics of topographically designed Smectic-A oily streaks

   https://doi.org/10.1039/d3sm00306j  

   Missaoui, Amine; Susser, Adam L; Aharoni, Hillel; Rosenblatt, Charles (May 2023, Soft Matter)

   (a) 3D visualization of a SmA divot measured by optical profilometry. (b) Polarized optical microscopy image showing the OS pattern between crossed polarizers, overlaid by the parameters used in our model. (c) Side view sketch showing the different parameters in our model. 

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3. Observation of a uniaxial ferroelectric smectic A phase

   https://doi.org/10.1073/pnas.2210062119  

   Chen, Xi; Martinez, Vikina; Nacke, Pierre; Korblova, Eva; Manabe, Atsutaka; Klasen-Memmer, Melanie; Freychet, Guillaume; Zhernenkov, Mikhail; Glaser, Matthew A.; Radzihovsky, Leo; et al (November 2022, Proceedings of the National Academy of Sciences)

   We report the observation of the smectic A F , a liquid crystal phase of the ferroelectric nematic realm. The smectic A F is a phase of small polar, rod-shaped molecules that form two-dimensional fluid layers spaced by approximately the mean molecular length. The phase is uniaxial, with the molecular director, the local average long-axis orientation, normal to the layer planes, and ferroelectric, with a spontaneous electric polarization parallel to the director. Polarization measurements indicate almost complete polar ordering of the ∼10 Debye longitudinal molecular dipoles, and hysteretic polarization reversal with a coercive field ∼2 × 10 5 V / m is observed. The SmA F phase appears upon cooling in two binary mixtures of partially fluorinated mesogens: 2N/DIO, exhibiting a nematic (N)–smectic Z A (SmZ A )–ferroelectric nematic (N F )–SmA F phase sequence, and 7N/DIO, exhibiting an N–SmZ A –SmA F phase sequence. The latter presents an opportunity to study a transition between two smectic phases having orthogonal systems of layers. 

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4. Chiral oily streaks in a smectic-A liquid crystal

   https://doi.org/10.1039/C6SM01238H  

   Nemitz, Ian R.; Ferris, Andrew J.; Lacaze, Emmanuelle; Rosenblatt, Charles (January 2016, Soft Matter)
5. A smectic liquid crystal model in the periodic setting

   https://doi.org/10.1016/j.na.2022.113187  

   Novack, Michael; Yan, Xiaodong (March 2023, Nonlinear Analysis)