The electron spectrum of the Hubbard model with coupling to pseudospin degrees of freedom

The model Hamiltonian describes the anharmonic vibrations of the apex oxygen atoms (O(4)) in YBaCuO-type superconductors by adding pseudospin degrees of freedom to the local part of a Hubbard Hamiltonian. The single-electron spectrum of this model is calculated self-consistently using a Green's function technique. We find additional subbands as a result of the added interaction accompanied by a destruction of electron-hole symmetry. Moreover, the system can develop hole conductivity at half filling which could be important for high temperature superconductivity in such materials.