Spectral density of the local Cu-O model

The local Cu-O model is a local version of the extended Hubbard model and corresponds to a two-channel Anderson impurity model in which the two channels correspond to screening and hybridizing channels, respectively, and the screening interaction, ${\mathrm{U}}_{\mathrm{dc}}$, is short range. The model represents a more realistic model for the local excitations in heavy fermions and may also be of relevance in understanding the normal state properties of high temperature superconductors. Below a critical screening strength, ${\mathrm{U}}_{\mathrm{dc}}$<${\mathrm{U}}_{\mathrm{dc}}^{\mathrm{crit}}$ the particle-hole symmetric model exhibits Fermi-liquid behavior, whereas for ${\mathrm{U}}_{\mathrm{dc}}$>${\mathrm{U}}_{\mathrm{dc}}^{\mathrm{crit}}$ a non-Fermi-liquid state forms. Here, we report results of a numerical renormalization group calculation for the spectral density of single-particle excitations, in both the Fermi-liquid and non-Fermi-liquid regimes. The Kondo resonance is strongly modified for ${\mathrm{U}}_{\mathrm{dc}}$ close to ${\mathrm{U}}_{\mathrm{dc}}^{\mathrm{crit}}$ and is destroyed for ${\mathrm{U}}_{\mathrm{dc}}$>${\mathrm{U}}_{\mathrm{dc}}^{\mathrm{crit}}$. The relevance of these results for high temperature superconductors and the photoemission spectra of heavy fermions is discussed.