Low frequency plasmonic state and negative permittivity spectra of coagulated Cu granular composite materials in the percolation threshold

We have studied the relative complex permittivity (epsilon(r) = epsilon(r)'-i epsilon(r)'') of copper granular composite materials containing coagulated Cu particles in the microwave range as well as the electrical conductivity. The insulator to metal transition was observed at the percolation threshold phi(c) = 16.0 vol. %. The enhancement of permittivity in the insulating state can be described by the Effective Cluster Model. Above the percolation threshold phi(c), it was found that the Cu granular composites show negative permittivity spectra below a characteristic frequency f(0) indicating the low frequency plasmonic state. Characteristic frequency tends to increase with particle content. (C) 2013 AIP Publishing LLC.