Failure of t-J models in describing doping evolution of spectral weight in x-ray scattering, optical, and photoemission spectra of cuprates

We have analyzed experimental evidence for an anomalous transfer of spectral weight from high-to low-energy scales in both electron-and hole-doped cuprates as a function of doping. X-ray scattering, optical, and photoemission spectra are all found to show that the high-energy spectral weight decreases with increasing doping at a rate much faster than predictions of the large U-limit calculations. The observed doping evolution is however well described by an intermediate coupling scenario where the effective Hubbard U is comparable to the bandwidth. The experimental spectra across various spectroscopies are inconsistent with fixed-U exact diagonalization or quantum Monte Carlo calculations, and suggest a significant doping dependence of the effective U in the cuprates.