Photoemission study of electronic states in with various doping levels

The temperature and doping dependences of photoemission spectra of polycrystalline (Formula presented) samples are investigated for several doping levels near the optimum (Formula presented) As doping increases, we observed a systematic shift of the core levels and an increase in the density of states at the Fermi level (Formula presented) Nonlinear shifts of the core levels with doping and a remarkable doping-dependent suppression of the spectral intensity over more than 300 meV below (Formula presented) are compatible with the reported results for (Formula presented) With decreasing temperature, the density of states was gradually suppressed at energies lower than 30 meV, suggesting a gap opening. The estimated leading edge shift is about 10 meV for all samples at both 20 and 105 K.