A universal high energy anomaly in the single particle spectral function is reported in three different families of high temperature superconductors by using angle-resolved photoemission spectroscopy. As we follow the dispersing peak of the spectral function from the Fermi energy to the valence band complex, we find dispersion anomalies marked by two distinctive high energy scales, E_1 approx 0.38 eV and E_2 approx 0.8 eV. E_1 marks the energy above which the dispersion splits into two branches. One is a continuation of the near parabolic dispersion, albeit with reduced spectral weight, and reaches the bottom of the band at the Gamma point at approx 0.5 eV. The other is given by a peak in the momentum space, nearly independent of energy between E_1 and E_2. Above E_2, a band-like dispersion re-emerges. We conjecture that these two energies mark the disintegration of the low energy quasiparticles into a spinon and holon branch in the high T_c cup rates.

We have performed an angle-resolved photoemission study of overdoped La1.78Sr0.22CuO4, and have observed sharp nodal quasiparticle peaks in the second Brillouin zone that are comparable to data from Bi2Sr2CaCu2O8+d. The data analysis using energy distribution curves, momentum distribution curves and intensity maps all show evidence of an electron-like Fermi surface, which is well explained by band structure calculations. Evidence for many-body effects are also found in the substantial spectral weight remaining below the Fermi level around (pi,0), where the band is predicted to lie above EF.