Normal State Properties of the Attractive Hubbard Model: Moment Approach

We introduce a two-delta-peak ansatz for the spectral density of the attractive Hubbard model in the normal state and in d-dimensions. The resulting two excitation branches and their weights are fixed in terms of the exact first four frequency moments. This ansatz correctly reproduces the atomic limit, the free case and the strong coupling limit to first order in the hopping amplitude. For this reason it is expected to provide a reasonable interpolation scheme covering the intermediate and strong coupling regimes for properties that do not depend sensitively on the damping of the two excitation branches. In the strong coupling regime, the upper excitation branch describes the creation of a fermion in an empty state, whereas the lower band arises from pair formation due to the creation of a fermion in a state already occupied by a fermion of opposite spin. Consequently, anomalous normal state properties can be expected whenever the chemical potential is within the correlation gap. This turns out to be the case when half-filling is approached for intermediate coupling as well as for any finite band filling in the strong coupling regime. In these filling and coupling regimes, there is no Fermi surface, and the formation and dissociation of pairs occur in the normal state as revealed by the temperature dependence of the double occupancy. For this reason the normal state properties exhibit an anomalous temperature dependence. Comparison with t-matrix calculations in the dilute and intermediate coupling.

By: T. Schneider, M. H. Pedersen and J. J. Rodriguez-Nunez (Univ. de Neuchatel, Switz.)

Published in: Zeitschrift fuer Physik Teil B, volume 100, (no 2), pages 263-76 in 1996

Please obtain a copy of this paper from your local library. IBM cannot distribute this paper externally.

Questions about this service can be mailed to .