Self-energy behavior away from the Fermi surface in doped Mott insulators.

We analyze self-energies of electrons away from the Fermi surface in doped Mott insulators using the dynamical cluster approximation to the Hubbard model. For large onsite repulsion, U, and hole doping, the magnitude of the self-energy for imaginary frequencies at the top of the band (k =(pi, pi)) is enhanced with respect to the self-energy magnitude at the bottom of the band (k =(0, 0)). The self-energy behavior at these two k-points is switched for electron doping. Although the hybridization is much larger for (0, 0) than for (pi, pi), we demonstrate that this is not the origin of this difference. Isolated clusters under a downward shift of the chemical potential, mu < U/2, at half-filling reproduce the overall self-energy behavior at (0, 0) and (pi, pi) found in low hole doped embedded clusters. This happens although there is no change in the electronic structure of the isolated clusters. Our analysis shows that a downward shift of the chemical potential which weakly hole dopes the Mott insulator can lead to a large enhancement of the (pi, pi) self-energy for imaginary frequencies which is not associated with electronic correlation effects, even in embedded clusters. Interpretations of the strength of electronic correlations based on self-energies for imaginary frequencies are, in general, misleading for states away from the Fermi surface.