Unveiling the broadband optical properties of Bi2Te3: Ultrahigh refractive index and promising applications

Abstract

van der Waals topological insulators, characterized by their high-index dielectric response, offer a promising materials platform for nanophotonics. Among these materials, Bi2Te3 has one of the highest refractive indices and extinction coefficients. However, the precise determination of Bi2Te3 optical properties remains challenging owing to its complicated physical model, which includes an oxide layer, topological conducting states, and optical anisotropy. Here, we resolve this problem and develop an accurate optical model for Bi2Te3 in a broad (450–1500 nm) spectral range. Our study shows that an oxide layer plays a major role in optical model for these wavelengths, while the influence of topological conducting states and optical anisotropy is minimal. Our model allows us to obtain accurate Bi2Te3 optical constants and demonstrate their use in biosensors, thermal theranostics, and topological phase singularities. Moreover, we observe a polarization transition of topological phase singularity for Bi2Se3, which opens a new direction for the development of topological phase effects. Therefore, our results open new avenues for photonic applications of Bi2Te3 optical properties.