Pairing correlations with s* and d(x(2)-y(2)) symmetry in a disordered Cu4O8 cluster

Recently we have shown [V. F. Elesin, A. V. Krasheninnikov, and L. A. Openov, Sov. Phys. JETP 79, 789 (1994)] that in the hole-doped Cu4O8 cluster pairing correlations with sk symmetry are nearly twice as strong as those with d(x2-y2) symmetry, while in the electron-doped cluster pairing correlations seem to be present in the s* channel only. In this paper the effect of on-site disorder on the pairing correlators with s* and d(x2-y2) symmetry in the Cu4O8 cluster is studied numerically through an exact diagonalization of the Emery-Anderson Hamiltonian. It is shown that at a nearly optimal doping level (0.25 excess holes per copper atom) the disorder weakens pairing correlations in the d(x2-y2) channel and has much less influence on pairing correlations in the s* channel. Based on the results obtained, the ''superconducting'' components of pairing correlators are estimated to be 10-30 % of their full values, with the remaining parts of correlators being contributions from a finite-size effect. These results indicate that cluster calculations may be relevant for the study of high-T-c superconductibility.