Ff. Assaad et al., FLUX-QUANTIZATION IN THE 2-DIMENSIONAL REPULSIVE AND ATTRACTIVE HUBBARD MODELS, Physical review letters, 71(12), 1993, pp. 1915-1918
In order to provide a numerical criterion for superconductivity, the g
round state energy E0(PHI) is calculated for the attractive and repuls
ive Hubbard models on a cylinder geometry threaded by a flux PHI. From
the functional form of E0(PHI), superconducting ground states may be
identified without prior knowledge of the pairing symmetry. E0(PHI) is
calculated with Monte Carlo methods. For the attractive Hubbard model
, our results confirm the existence of a superconducting ground state.
In contrast, our results show that the quarter-filled repulsive Hubba
rd model is not superconducting and that a Hartree-Fock paramagnetic a
pproximation fits the data very well.