We report the first observation of surface plasmons in a granular metal. The plasma frequency ${\omega }_p$ in the Ag-Si${\mathrm{O}}_2$ system is determined from plasma resonance absorption measurements over the entire range of composition from the continuous-metal-film limit to the isolated-metal-particle limit. The observed decrease in ${\omega }_p$ with increasing insulator concentration is understood within the framework of the phenomenological Maxwell-Garnett theory.

• Received 29 January 1975

DOI:https://doi.org/10.1103/PhysRevB.12.2121