Universality of single-particle spectra of cuprate superconductors.

All the available data for the dispersion and linewidth of the single-particle spectra above the superconducting gap and the pseudogap in metallic cuprates for any doping have universal features. The linewidth is linear in energy below a scale omega(c) and constant above. The cusp in the linewidth at omega(c) mandates, due to causality, a waterfall, i.e., a vertical feature in the dispersion. These features are predicted by a recent microscopic theory. We find that all data can be quantitatively fitted by the theory with a coupling constant lambda(0) and an upper cutoff at omega(c), which vary by less than 50% among the different cuprates and for varying dopings. The microscopic theory also gives these values to within factors of O(2).