High-Index Topological Insulator Resonant Nanostructures from Bismuth Selenide

TL;DR

This study investigates the optical properties of Bi2Se3 topological insulator nanostructures, revealing high refractive indices and Mie resonances, which could enable advanced photonic and quantum device applications.

Contribution

It provides the first detailed optical characterization of Bi2Se3 nanobeams, demonstrating their support for MIR Mie-resonances and phase shifts, with implications for photonics and quantum technologies.

Findings

Refractive index up to ~6.4 in MIR range

Support for Mie-resonances in nanobeams

Observation of up to 2π phase shift across resonances

Abstract

Topological insulators (TIs) are a class of materials characterized by an insulting bulk and high mobility topologically protected surface states, making them promising candidates for future optoelectronic and quantum devices. Although their electronic and transport properties have been extensively studied, their optical properties and prospective photonic capabilities have not been fully uncovered. Here, we use a combination of far-field and near-field nanoscale imaging and spectroscopy, to study CVD grown Bi2Se3 nanobeams (NBs). We first extract the mid-infrared (MIR) optical constants of Bi2Se3, revealing refractive index values as high as n ~6.4, and demonstrate that the NBs support Mie-resonances across the MIR. Local near-field reflection phase mapping reveals domains of various phase shifts, providing information on the local optical properties of the NBs. We experimentally measure up to 2{\pi} phase-shift across the resonance, in excellent agreement with FDTD simulations. This work highlights the potential of TI Bi2Se3 for quantum circuitry, non-linear generation, high-Q metaphotonics, and IR photodetection.