Tunneling percolation behavior and filling factors in metal-insulator nanocomposites

We have studied conventional transport and tunneling in nanocomposite metal-insulator systems. Two types of percolation thresholds P$_{\mathrm{C}}^{1}$ and P$_{\mathrm{C}}^{2}$, associated with both conventional transport and quantum tunneling respectively are identified in the same nanocomposite systems and the functional dependence between the two thresholds is investigated. In addition, we have studied the relationship between filling factors and percolation thresholds, particularly the importance of geometric effects of nanoparticles of different sizes and shapes in metal-insulator composite systems. A non-monotonic dependence of filling factor as a function of filler volume fraction is established and possible implications of this non-trivial behavior is discussed.