Structural and Angle-Resolved Optical and Vibrational Properties of Chiral Topological Trivial Insulator InSeI

Chiral materials, also known as helical materials, have recently gained significant attention due to their distinct structural and quantum properties. InSeI, in particular, has emerged as an exciting chiral topological trivial insulator with theoretically predicted exotic properties. In this work, I present a scalable growth technique for synthesizing high-quality single-crystal InSeI and establish its optical, structural, and vibrational properties through microscopy and spectroscopy techniques. Using the Bridgman crystal growth technique, I have successfully produced centimetersized chiral InSeI crystals for the first time. These crystals exhibit higher structural quality and easier exfoliation characteristics compared to those grown using conventional solid-state techniques. The Bridgman-grown crystals demonstrate high tolerance to lightinduced degradation effects due to a significantly reduced defect concentration. Microscopy studies confirm the excellent chiral structural characteristics of InSeI, while the first in-situ nanometer spatial resolution electron energy loss spectroscopy (EELS) measurements establish their bandgap at 2.08 eV, which aligns with the cryogenic photoluminescence (PL) emission peak. Angle-resolved Raman spectroscopy, combined with calculated vibrational properties, reveals that InSeI sheets possess Raman modes in five distinct frequency regions. These modes are primarily associated with In-, In-I, InSe-I, and Se-atomic motions and show dramatic changes in relative intensities under different polarization vector orientations. Overall, my results introduce a practical method for realizing high-quality InSeI and offer detailed experimental insights into its structural, optical, and vibrational properties. This research advances the fundamental knowledge of chiral material systems, highlighting the potential of InSeI in various technological applications.