Spin-cluster states inCuO2planes

Abstract
When doping the antiferromagnetically ordered high-Tc cuprates with holes magnetic polarons (spin-polarized clusters) are formed. We discuss two different mean-field approaches of the three-band Hubbard model to calculate the binding energy and polarization of the clusters. At higher hole concentrations and due to cluster diffusion a phase separation is formed by establishing large fractal or percolative clusters. This percolation picture allows us to understand experimentally obtained results for phase separation as well as magnetic and conductive phase diagrams.