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 PtSe₂optically 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.