Superconductivity in an attractive two-band Hubbard model with second nearest neighbors

This work extends the calculations performed by G. Litak, T. Örd, K. Rägo, and A. Vargunin, Physica C 483, 30 (2012), by including second nearest neighbors in an attractive two-orbital Hubbard model. We assumed that both the intra-orbital (Ui, i, with i=1,2) and the inter-orbital Hubbard correlations (Ui, j, with i ≠ j) are negative; namely, Ui, j ≤ 0, ∀(i, j). We calculated the T−n phase diagram in the mean-field approximation. For a finite chemical potential ξ10 and a certain second nearest-neighbor parameter t2 superconductivity develops in two dome-like regions, each of which has its own energy gap. Notoriously, for t2/|t1|=0.70 and ξ10/|t1|=3, where t1 is the nearest-neighbor parameter, Tc becomes zero around n=2.5.