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Comment: (ps version of the dvi file, resubmitted because previous uucompressed version was corrupted), 9 pages
Comment: seven pages, nine figures as ps files. Accepted in Int. J. Modern Phys. C (1997)
We explore the effect of the imaginary part of the self-energy, $Im\Sigma(\vec{k},\omega)$, having a single pole, $\Omega(\vec{k},\omega)$, with spectral weight, $\alpha(\vec{k})$, and quasi-particle lifetime, $\Gamma(\vec{k})$, on the density of states. We solve the set of parameters, $\Omega(\vec{k},\omega$), $\alpha(\vec{k})$, and $\Gamma(\vec{k})$ by means of the moment approach (exact sum rules) of Nolting. Our choice for $\Sigma(k,\omega)$, satisfies the Kramers - Kronig relationship automatically. Due to our choice of the self - energy, the system is not a Fermi liquid for any value of the interaction, a result which is also true in the moment approach of Nolting without lifetime effects. By increasing the value of the local interaction, $U/W$, at half-filling ($\rho = 1/2$), we go from a paramagnetic metal to a paramagnetic i...
Comment: 6 pages, revtex, to be published in Helvetica Physica Acta
We derive the superconductiong mean-field equations for an attractive interaction, V, in the s-wave channel when local Coulomb interactions are taken into account for any value of U. Our results show that the Coulomb repulsion is detrimental to the critical temperature, $T_c$, and the order parameter, $\Delta(T)$, for values of $U \geq |V|$. Furthermore, our results depend on band filling in a sensible way. In the presence of local correlations, $2\Delta(0)/T_c$ differs from the BCS ratio, since Coulomb interactions affect much more the superconducting critical temperature, $T_c$, than the superconducting order parameter, $\Delta(T)$. We conclude that the presence of Coulomb interactions play an additional role in the analysis of experimental data, specially in narrow band systems.
Comment: 8 pages, 3 figures (2 ps files for Fig. 2) To appear in Physica A
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