Enantiomeric Ferroelectric Chiral Domains

Chiral ferroelectric crystals with inherent chirality and spontaneous polarization have recently gained considerable interest. However, the chiral topological texture, which provides a promising platform for exploring exotic functionalities, has never been found in enantiomeric ferroelectric crystals. Here, we report a pair of enantiomeric molecular ferroelectrics, [RFAO][ReO₄] and [SFAO][ReO₄] (RFAO/SFAO = (4R,5R/4S,5S)-4-fluoro-1-azabicyclo[3.2.1]octane). The enantiomers crystallize in the chiral-polar point group 2 at room temperature and undergo two ferroelectric phase transitions with an Aizu notation of 222F2 at 350 K and 432F2 at 463 K, respectively. Such phase transitions enable them to show a multistep switchable second-harmonic generation circular dichroism (SHG-CD) effect from high to low to off (inactive) SHG-CD states. More importantly, we observed spiral chiral ferroelectric domains in the enantiomers. To the best of our knowledge, this is the first discovery of chiral domains in enantiomeric ferroelectric crystals. Our breakthrough findings give new sights into the interplay between polarization and chirality and will greatly stimulate further exploration of chiral ferroelectric crystals with switchable SHG-CD and chiral domains for next-generation electronic-photonic devices.