Hyperbolic Phonon Polaritons in a Van der Waals Nanowire: Effects of Size and Dielectric

Hyperbolic materials (e.g., h‐BN, ‐MoO 3 ) support phonon polaritons (PhPs) with superior properties, including high wavelength compression, long lifetime, low propagation loss, and making them highly attractive in the field of nanophotonics. However, the influences of confined dimensions, nanoscale size, and dielectric environment on the characteristics of PhPs remain insufficiently understood. Taking h‐BN van der Waals (vdW) nanowires (NWs) as a model system, we systematically investigate how NW size and dielectric environment modulate the dispersion spectra, wavelength compression ratios, and group velocities of hyperbolic PhPs. Numerical calculations reveal that, in contrast to quasi‐2D vdW slabs, the group velocities of PhPs in the upper and lower reststrahlen bands of quasi‐1D h‐BN are completely opposite. This finding indicates that confined dimensions significantly alter the dispersion behaves and related properties of hyperbolic PhPs in vdW nanostructures. Further analysis shows that NW size exerts a remarkable regulatory effect on PhP dispersion spectra, wavelength compression ratios, and group velocities. While the dielectric constant of the surrounding medium significantly affects dispersion spectra and group velocities, its impact on the wavelength compression ratio is extremely weak; the underlying physical mechanism is analyzed in depth.