Curvature-determined enhancement of far-infrared absorption in metallic nanoparticles

We investigate the role of nanoscale surface geometry in the far-infrared absorption in metallic nanoparticles. In the quasistatic regime, electromagnetic dissipation can be expressed through a surface representation in which the absorbed power is determined by the spatial distribution of the electric field at the particle boundary. We show that regions of small local curvature strongly amplify both normal and tangential components of the electric field, leading to a geometric enhancement of absorption. For particles with minimal curvature radius rc, the electric dipole contribution scales approximately as αEeff∼αE(0)R/rc, where αE(0) is the Drude contribution and R is the particle radius. In addition, surface roughness induces an effective anisotropic conductivity in a thin near-surface layer, allowing tangential electric fields to drive surface currents. This provides an additional dissipation channel which can exceed the conventional magnetic dipole absorption in the far-infrared regime. The predicted enhancement is consistent with experimental observations of excess absorption in metallic nanoparticles. The results indicate that nanoscale surface curvature acts as a fundamental geometric parameter governing electromagnetic dissipation in metallic nanostructures.