AN INVESTIGATION OF THE 2D ATTRACTIVE HUBBARD-MODEL

We present an investigation of the 2D attractive Hubbard model, consid ered as an effective model relevant to superconductivity in strongly i nteracting electron systems. We use both hybrid Monte-Carlo simulation s and existing hopping parameter expansions to explore the low tempera ture domain. The increase of the static S-wave pair correlation with d ecreasing temperature, which depends weakly on the band filling in the explored temperature range, is analyzed in terms of an expected Koste rlitz-Thouless superconducting transition. Using both our data and pre viously published results, we show that the evidence for this transiti on is weak: If it exists, its temperature is very low. The number of u npaired electrons remains nearly constant with temperature at fixed at tractive potential strength. In contrast, the static magnetic suscepti bility decreases fast with temperature, and cannot be related only to pair formation. We introduce a method by which the Pade approximants o f the existing series for the susceptibility give sensible results dow n to rather low temperature region, as shown by comparison with our nu merical data.