The spin-imbalanced attractive Hubbard model in d = 3: Phase diagrams and BCS–BEC crossover at low f
We study the superconducting properties of the spin-imbalanced attractive Hubbard model (AHM) in the presence of a Zeeman magnetic field, using the broken symmetry Hartree approximation, mostly in the low density case. The evolution from the weak coupling (BCS-like limit) to the strong coupling limit of tightly bound local pairs (LP) with increasing attraction, at T=0 is investigated for d=3, both for the case of a fixed chemical potential and for a fixed number of particles. Also the influence of the spin-dependent Hartree term on the phase diagrams at T≠0 at weak coupling is studied and reentrant transition is found, which is demonstrated in the temperature characteristics of the order parameter and magnetization. The BCS–BEC crossover diagrams in the presence of a Zeeman magnetic field in three dimensions for simple cubic (sc) lattice are investigated and the results are compared with those obtained in the other lattice geometries.