Large Non-Adiabatic Hole Polarons and Matrix Element Effects in the Angle-Resolved Photoemission Spectroscopy of Dielectric Cuprates

Abstract

We propose a generalization of the conventional theory based on the assumption of the well-isolated Zhang-Rice 1A1g singlet to be a first electron-removal state in insulating copper oxide. The photohole is assumed to be localized on either small (pseudo) Jahn-Teller (PJT) polaron or large non-adiabatic polaron-enclosed one or four to five CuO4 centers, respectively, with active one-center valent (1A1g-1,3Eu) manifold. In the framework of the cluster model we have performed the model microscopic calculation of the k-dependence of the matrix element effects and photon polarization effects for the angle-resolved photoemission (ARPES) in insulating cuprates like Sr2CuO2Cl2. We show that effects like the "remnant Fermi surface" detected in the ARPES experiment for Ca2CuO2Cl2 may be, in fact, the manifestation of the matrix element effects rather than of the original band-structure Fermi surface or strong antiferromagnetic correlations. The measured dispersion-like features in the low-energy part of the ARPES spectra may be the manifestation of the complex momentum-dependent spectral line shape of the large PJT polaron response, in addition to the dispersion effect for the well-isolated Zhang-Rice singlet in antiferro-magnetic matrix. © 2002 Elsevier Science B.V. All rights reserved.