Evolution of the fermi surface of cuprates on the basis of the spin-polaron approach

A spin-polaron approach is proposed for describing the evolution of the Fermi surface (FS) and the electronic structure of cuprates with various doping levels on the basis of the spin-fermion model. The complexity of the internal structure of a spin polaron is taken into account by introducing the superposition of spin-polaron states with various radii, while doping is effectively described by frustration in the spin Hamiltonian. The calculations of the polaron spectrum, the spectral weight of bare charge carriers, and the Fermi surface demonstrate radical changes in the electronic structure upon an increase of the doping level. The results obtained make it possible to use a unified approach for describing the experimental data on photoemission such as the isotropic bottom of the band and the residual Fermi surface of undoped compounds, the large Fermi surface and the extended saddle-type singularity for optimally doped compounds, as well as the pseudogap in the case of intermediate doping. (C) 2001 MAIK Nauka/ Interperiodica.