We have studied the effects of strong impurity scattering on disordered superconductors beyond the low-impurity concentration limit. By applying the full coherent potential approximation to a superconductiong A-B binary alloy, we calculated the fluctuations of the local order parameters ${\Delta }_A,{\Delta }_B$ and charge densities $n_A{,n}_B$ for weak and strong on-site disorder. We find that for narrow band alloy s-wave superconductors the conditions for Anderson’s theorem are satisfied in general only for the case of particle-hole symmetry. In this case it is satisfied regardless of whether we are in the weak or strong scattering regimes. Interestingly, we find that strong scattering leads to band splitting, and in this regime for any band filling we have a critical concentration where a superconductor-insulator quantum phase transition occurs at $T=0.\mathrm{}$

• Received 1 August 2000

DOI:https://doi.org/10.1103/PhysRevB.63.024501