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The attractive Hubbard model

A study of the attractive Hubbard model by means of the COM is reported in Refs. [76,77,78]. In particular the following properties have been computed:

  1. The thermodynamic properties (i.e., double occupancy, crossover temperature, chemical potential) [76,77,78]

  2. The single-particle properties (i.e., density of states) [77,78]

  3. The response functions (i.e., spin susceptibility) [76,77,78]

The COM results have been compared with the ones obtained by:

The Hubbard model with on-site attractive interaction has been studied by means of the Composite Operator Method. At zero temperature, when the strength of the attractive interaction equals the bandwidth, the system exhibits a phase transition to a pair state, where all the electrons are locally paired [76]. The temperature $ T_{p}$ which controls the crossover to the pair state is calculated as a function of $ U$. Some properties, as the double occupancy and the spin magnetic susceptibility [78], show a good agreement with numerical data. For strong attractive interaction the static uniform susceptibility is strongly depressed; increases by increasing $ T$ and tends to zero as $ T\longrightarrow T_{p}$. Analytical and numerical calculations show that there is a critical value of the interaction, $ U_{c}$, where the system exhibits a metal-insulator transition. At zero temperature it is found that $ U_{c}=-W$, where $ W$ is the bandwidth [77].


next up previous
Next: The t-t'-U model Up: contents Previous: Ladders and Layers
avella 2002-06-10