Data-driven Discovery of Chiral Materials with Soft Optical Phonons

Chiral solids present exciting opportunities for spintronic, sensing, and optical applications by enabling unique interactions with circularly polarized light and chiral materials. Materials exhibiting soft (low-frequency) optical phonons are particularly promising for terahertz (THz) technologies, yet only a few chiral systems with such characteristics are known. Here, we combine data mining, machine learning (ML), and density functional theory (DFT) calculations to identify chiral materials with optical phonon frequencies in the low-THz range. Screening the Materials Project database and performing first-principles phonon calculations, we identified more than 140 chiral, non-oxide compounds exhibiting low-frequency optical modes on the order of a few THz. Our ML analysis reveals that these materials often contain large p-block anions, which promote softer phonon modes. Raman spectroscopy measurements further validate our predictions by confirming the phonon density of states in newly characterized chiral crystals, including Na₃SbS₃, Na₃SbSe₃, and CsCuBr₃. Finally, we discuss the chiral phonon modes observed in these compounds and their implications for future THz and quantum device design.