ETA-SUPERCONDUCTIVITY IN THE ONE-DIMENSIONAL PENSON-KOLB MODEL

Using exact Lanczos diagonalizations we have studied in detail the tra nsition into the eta-superconducting state in the Penson-Kolb model. W e have shown that the transition occurs at any band filling and the cr itical value W-c, varies between W-c similar or equal to 1.8t at half- filling to W-c similar or equal to -2t for two particles on the lattic e, The transition corresponds to abrupt and drastic change in the grou nd-state structure. After the transition the contribution of the one-e lectron band to the ground-state energy is almost suppressed.