Abnormal Absorption and Energy Flow of Electromagnetic Wave in Ultrathin Metal Films

Abstract

Recently nonlocal optical responses of metal nanostructures have been investigated to better describe the abnormal optical properties of structures within a feature length of 10 nm. However, most of the investigations are based on hydrodynamical Drude model. In the present work, on the basis of the quantum nonlocal response, we study properties of s-polarization electromagnetic waves in metal films. In the studies of the dependence of absorption on frequency and thin film thickness, we find that in the case of no plasmon excitations and any scattering experienced by electrons in the system, the nonlocal response theory still gives a considerable energy absorption caused by electron–hole pair excitations. However, both the local Drude model and hydrodynamical Drude model only present zero absorption in this case. In addition, our calculation shows that the energy flow of the nonlocal-response theory displays an anomalous oscillation in the film, which is ascribed to the negative work done by electric field in some regions of the film. This is just the manifestation for the nonlocal response of current to the field.