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-consistent equations is solved in the real-frequency domain to avoid the analytic continuation procedure. By tuning the chemical potential the particle density was varied in the limits 0.01 < n < 0.18. For the value of the attractive potential U=8t the binding energy of pairs monotonically decreases with increasing n, from its zero-density limit 2.3t and vanishes at a critical density n=0.19. A pairing-induced pseudogap in the single-particle density of states is found at low densities and temperatures. 
Bumsoo Kyung (Max Planck Institute), E. G. Klepfish (King's College)   and P. E. Kornilovitch (Max Planck Institute)