Phase diagram and BCS–Bose condensation crossover in 1D and 2D Hubbard models

• Published in: Physica. C, Superconductivity Vol. 364; pp. 131 - 133
• Main Authors: Kocharian, A.N., Yang, C., Chiang, Y.L.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2001
• Subjects: BCS–BC crossover; Bethe-ansatz; Hubbard model; Quantum Monte-Carlo; 71.10.Fd; BCS–BC crossover; Bethe-ansatz; Quantum Monte-Carlo; 74.20.−z; Hubbard model; 74.20.Fg
• ISSN: 0921-4534; 1873-2143
• DOI: 10.1016/S0921-4534(01)00730-4

The ground-state energy, the concentration of double occupied sites and the density of bound electron pairs in low-dimensional attractive Hubbard model are calculated by means of the generalized self-consistent field (GSCF) approach. This approach gives an excellent agreement with the corresponding Bethe-ansatz solution and the quantum Monte-Carlo calculations in a wide range of interaction strength U<0 and electron concentration n. A simple relationship is found between the order parameter and the density of bound electron pairs, valid for any dimension and in entire parameter space U, n and magnetic field h. The electron pairing and the crossover from the itinerant BCS regime into the Bose condensation regime of local pairs are studied in dependence of both U and n. The GSCF theory correctly displays the separation of the energy gap from the BCS order parameter at n≠1 as | U| increases.