Angle-resolved photoemission spectroscopy of Sr2CuO2Cl2 - art. no. 014505

We have investigated the lowest binding-energy electronic structure of the model cuprate Sr2CuO2Cl2 using angle-resolved photoemission spectroscopy. O ur data from about 80 cleavages of Sr2CuO2Cl2 single crystals give a compre hensive, self-consistent picture of the nature of the first electron-remova l state in this model undoped CuO2-plane cuprate. First, we show a strong d ependence on the polarization of the excitation light which is understandab le in the context of the matrix element governing the photoemission process , which gives a state with the symmetry of a Zhang-Rice singlet. Secondly, the strong, oscillatory dependence of the intensity of the Zhang-Rice singl et on the exciting photon energy is shown to be consistent with interferenc e effects connected with the periodicity of the crystal structure in the cr ystallographic direction. Thirdly, we measured the dispersion of the first electron-removal states along Gamma--> (pi, pi) and Gamma--> (pi ,0), the l atter being controversial in the literature, and have shown that the data a re best fitted using an extended tJ model, and extract the relevant model p arameters. An analysis of the spectral weight of the first ionization state s for different excitation energies within the approach used by Leung et al . [Phys. Rev. B 56, 6320 (1997)] results in a strongly photon-energy depend ent ratio between the coherent and incoherent spectral weight. The possible reasons for this observation and its physical implications are discussed.