Time-dependent Gutzwiller theory of pair fluctuations in the Hubbard model

The time-dependent Gutzwiller approximation (TDGA) is extended towards the inclusion of pair correlations. As a first application and in order to check the quality of the method we evaluate superconducting phase transitions in the attractive Hubbard model. It turns out that the TDGA can capture the crossover from weak to strong coupling and that the temperature scale of the intermediate regime is in good agreement with Quantum Monte Carlo calculations in contrast to the BCS approximation. In case of particle-hole symmetry we show the consistency of the approach from the degeneracy of both particle-particle- and particle-hole-channels. (c) 2007 Elsevier B.V. All rights reserved.