Nonlocal Effects in the Optical Response of Metal Nanoparticles

Abstract

Spatial nonlocality is known to play an important role at distances of a few nanometers, but few efforts have been made to theoretically investigate nonlocal effects in a rigorous way. We explore the effect of nonlocal response, which can be critical in the optical performance of metals at distances of 1–2 nanometers. This is particularly significant in situations for which small regions dominate the response of a larger structure. We present two different approaches to account for nonlocality in metal nanoparticles: (i) the non‐retarded specular reflection model (SRM) and (ii) the fully retarded hydrodynamical model. Comparison with available experiments results in excellent agreement with our parameter‐free modelling of nonlocal effects, which produce dramatic changes with respect to the customary local theory. We show that nonlocal effects in both models produce sizable plasmon blue shift and broadening in single metal nanoparticles as well as in dimers and shell structures. The hydrodynamical model in particular offers a way to include smooth electron distributions at surfaces and is therefore a competitor to ab initio methods.