Low-lying excitations of a strongly correlated superconducting state: role of correlation in the ARPES experiments for cuprates

Motivated by recent photoemission experiments on cuprates, the low-lying excitations of a strongly correlated superconducting state are studied numerically. It is observed that along the nodal direction these low-lying one-particle excitations show a linear momentum dependence for a wide range of excitation energies and, thus, they do not present a kink-like structure. The nodal Fermi velocity $v_{\rm F}$, as well as other observables, are systematically evaluated directly from the calculated dispersions, and they are found to compare well with experiments. It is argued that the parameter dependence of $v_{\rm F}$ is quantitatively explained by a simple picture of a renormalized Fermi velocity. The intimate correlation between quasi particle weight and the superconducting ordering is also discussed. [1] S. Yunoki, E. Dagotto, and S. Sorella, preprint (2004).