Electrically Tunable Heliconical Smectic Superstructure in Polar Fluids

Abstract

The ferroelectric nematic (NF) phase and related polar liquid-crystalline phases form a new class of strongly polarized yet fluid soft matter. Well-recognized heliconical ferroelectric phases such as NTBF and SmC_P^H exist, but their electro-optic functionality in smectic systems has been largely unexplored. Here, we report a newly designed single-component achiral molecule exhibiting a hierarchical polar phase sequence: SmAF-NTBF-HEC-SmC_P^H. The key feature of the SmC_P^H phase is its ability to form a stable macroscopic orientation without any alignment layers and to enable continuous, reversible pitch modulation over a wide spectral range at ultralow electric fields, approximately one-third of those required for conventional heliconical nematics. The system exhibits characteristic electro-optic properties in the sub-kilohertz range, differentiating it from heliconical materials controlled by dielectric-elastic balance at higher frequencies. In addition, the SmC_P^H phase's polar heliconical smectic structure facilitates enhanced second-harmonic generation via favorable phase matching, thereby establishing a simple and robust platform for low-voltage photonic applications.