Nonuniversal breakdown behavior in superconducting and dielectric composites

We discuss the critical current density $J_c$ of composites where a fraction p of the material is superconducting and the dielectric breakdown electric field $E_c$ of composites where a fraction p of the material is metallic. Both of these nonlinear processes are characterized by power-law behavior near the percolation threshold $p_c$, $J_c$∝(p-$p_c$ ${)}^v$ and $E_c$∝($p_c$-p${)}^y$. The exponents v and y are nonuniversal, depending strongly on both the dimensionality and microstructure of the composite.