A universal high energy anomaly in angle resolved photoemission spectra of high temperature superconductors - possible evidence of spinon and holon branches

A universal high energy anomaly in the single particle spectral function is reported in three dierent 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, E1 0.38 eV and E2 0.8 eV. E1 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 point at 0.5 eV. The other is given by a peak in the momentum space, nearly independent of energy between E1 and E2. Above E2, 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 Tc cuprates.