Comparison of Effective Models for CuO₂ Layers in Oxide Superconductors

Abstract

Several effective models, as derived from a general two-band Hubbard model for CuO₂ layers in oxide superconductors are studied. In particular we compare the Hubbard model with the hole-spin models (unsymmetrized and symmetrized) and a generalized effectice single-band (t-J) model.¹ Our exact diagonalization results for a finite CuO₂ chain of 4 cells show that spectral properties of a single mobile quasiparticle in a general Hubbard model can be well reproduced by reduced effective models. This remains valid even in the mixed valence regime, where the straightforward derivation of the hole-spin model is not possible due to the breakdown of the perturbation expression using hopping parameter in the Hubbard model as a small parameter.