Low-frequency divergence of the dielectric constant in metal-insulator nanocomposites with tunneling

Dielectric measurements were done on cosputtered metal-insulator nanocomposite films with metal volume fraction above the metal-insulator transition, in the frequency range between 20 Hz and 30 MHz. At intermediate and high frequency, the dielectric function can be qualitatively described in terms of the percolation theory. In the low-frequency region, we observe a sharp relaxation-type increase of the real part of dielectric constant with decreasing frequency, while the imaginary part is dominated by dc conductivity. We suggest that the low-frequency behavior may be due to a combination of metallic and tunneling conduction in the system.