Edge-orientation dependent nanoimaging of mid-infrared waveguide modes in high-index PtSe₂

Abstract

All-dielectric nanophotonics is a rapidly developing field that employs high-index low-loss dielectric materials to boost light–matter interactions at the nanoscale. This is owing to their potential in achieving low-loss optical responses and the coexistence of strong enhancement of electric and magnetic fields, which are absent in their plasmonic counterparts. Transition-metal dichalcogenides (TMDCs) have been utilized for high-index dielectric Mie nanoresonators in the visible to near-infrared spectral range due to their high in-plane and out-of-plane optical anisotropy, excitonic effect, and high-index properties. However, high-index materials for mid-infrared (MIR) nanophotonics are still highly sought after. Here, it is shown that PtSe₂, a group-10 TMDC, could support dielectric waveguide modes in MIR despite its semimetallic nature. It is revealed that PtSe₂ optically acts as a dielectric material with a high refractive index of ≈5 and a low extinction coefficient in the MIR region. The value is among the highest in the low-loss TMDCs and mainstream dielectric materials. A comprehensive sample-edge-orientation dependent nanoimaging together with spectroscopic nanoimaging characterization of the PtSe₂ allows the extraction of the dispersion relations of the modes, from which the velocity parameters could be determined. This work paves the way for high-performance MIR devices via high-index PtSe₂-based nanostructures.