Nature of the Pseudogap Phase of HTSC Cuprates

Abstract

The pseudogap phase of HTSC cuprates is associated with the formation of a system of quantum electron–hole (EH) dimers similar to the Anderson RVB phase. A specific role of the electron–lattice relaxation in the formation of metastable EH dimers in cuprates with the T and T  ' structures is considered. An effective spin–pseudospin Hamiltonian of the CuO₂ plane of cuprate is introduced in the model of charge triplets and S = 1 the pseudospin formalism. In the molecular-field approximation (MFA), for the coordinate representation, the main MFA phases have been found: antiferromagnetic insulator, charge density wave, boson superconductor with the d-symmetry of the order parameter, and two metallic Fermi-phases that form the “strange”-metal phase. MFA is shown to enable, as a whole, a proper description of the features of the phase diagrams typical of cuprates. As in the case of typical s = 1/2 quantum antiferromagnet, the actually observed cuprate phases such as the charge ordering and the superconductivity reflect a “physical” ground state close to MFA phases but with strongly reduced values of local order parameters.