Tensor-product structure of a new electromagnetic propagator for nonlocal surface optics of metals

Abstract

With emphasis on the physical interpretation, the structure of a recently constructed electromagnetic propagator describing, within the framework of the semiclassical infinite-barrier model, the nonlocal optical properties of adjacent vacuum-metal half-spaces, is analyzed. The tensor-product structure of the rotational-free and divergence-free parts of the propagator is determined, and the direct, the indirect, and the self-field contributions are identified. On the basis of a plane-wave expansion, the physical role of the different propagator terms is studied. The contributions to the propagator from the collective polariton and plasmon excitations are separated from those stemming from the electron-hole pair excitations. Via a damped-wave picture of the propagator, contact with a new local propagator formalism of Sipe is established. The flexibility of the present formalism is demonstrated by investigating (i) the excitation of nonlocal surface waves by an oscillating dipole and (ii) the concept of surface-dressed dipole polarizability in the nonlocal regime.