Localized surface plasmons in a Weyl semimetal nanosphere

Abstract: In this study, we investigate the localized surface plasmon modes of a sub-wavelength spherical nanoparticle composed of a Weyl semimetal, taking into account the axion modification of electrodynamics. We derive analytical solutions for dipole and quadrupole normal modes by employing the quasistatic approximation. The axion term leads to modified Fr\"ohlich conditions, resulting in multiple non-degenerate plasmonic resonances with distinct polarization dependencies. In contrast to isotropic conventional metals, the magnetoelectric properties of Weyl semimetals enable an incident electromagnetic field, with the electric field transverse to the surface of the sphere, to excite a localized surface plasmon.