DENSITY-INDUCED BREAKING OF PAIRS IN THE ATTRACTIVE HUBBARD-MODEL

A conserving T-matrix approximation is applied to the two-dimensional attractive Hubbard model in the low-density regime. A set of self-cons istent equations is solved in the real-frequency domain to avoid the a nalytic continuation procedure. By tuning the chemical potential the p article density was varied in the limits 0.01 < n < 0.18. For the valu e of the attractive potential Ci = 8t the binding energy of pairs mono tonically decreases with increasing n, from its zero-density limit 2.3 t, and vanishes at a critical density n(cr) = 0.19. A pairing-induced pseudogap in the single-particle density of states is found at low den sities and temperatures.