Strong nonlocal contributions to Cu 2p photoelectron spectroscopy

Calculations of Cu 2p photoelectron spectra for a Cu₃O₁₀ cluster with a reduced basis set show that the introduction of more Cu sites leads to a revised interpretation of the Cu 2p spectrum. Besides the usual peaks of mainly 3d⁹ and 3d¹⁰L character another peak appears at lower binding energy. This peak is of mainly 3d¹⁰ character. The hole has moved away from the core hole potential and has formed a Zhang-Rice singlet on a neighboring CuO₄ unit. This effect explains the asymmetric line shape of the main line in the Cu 2p spectra of CuO and the high-T_c compounds. For formally trivalent copper compounds, such as NaCuO₂, this effect disappears and a narrow line shape is observed. The consequences of hole doping (33%) on the Cu 2p spectra have also been studied. The peak assignment turns out to be very similar to that of the undoped system.