Structural and angle-resolved optical and vibrational properties of chiral trivial insulator InSeI

Chiral materials, known for their unique structural and quantum properties, have garnered significant interest, with InSeI emerging as a promising chiral topologically trivial insulator. In this study, we introduce a scalable Bridgman crystal growth technique to synthesize large, environmentally stable single crystals of InSeI, achieving centimeter-sized chiral crystals with superior quality. Notably, this work marks the first report of photoluminescence (PL) emission from exfoliated InSeI chiral chains, alongside a detailed exploration of their polarization-dependent optical and phononic properties. Our Bridgman-grown crystals exhibit excellent structural integrity, enhanced exfoliation characteristics, and increased resistance to light-induced degradation compared to those produced by traditional solid-state methods. A microscopy analysis confirms the distinct chiral structure of InSeI, and the first in situ nanometer spatial resolution electron energy loss spectroscopy measurements establish a bandgap of 2.08 eV, consistent with the cryogenic PL emission peak. Angle-resolved Raman spectroscopy, combined with calculated vibrational properties, identifies five distinct frequency regions in the Raman modes, predominantly associated with In-, In-I, In-Se-I, and Se-atomic motions, with significant intensity variations under different polarization orientations. This study not only offers a practical method for synthesizing high-quality InSeI but also provides the first comprehensive experimental insights into its unique optical and vibrational properties, significantly advancing the understanding of chiral material systems.