Nature of the Pseudogap Phase of HTSC Cuprates
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Nature of the Pseudogap Phase of HTSC Cuprates A. S. Moskvina, * and Yu. D. Panova a Ural
Federal University Named after the First President of Russia B.N. Yeltsin, Yekaterinburg, 620002 Russia *e-mail: [email protected] Received March 26, 2020; revised March 26, 2020; accepted April 2, 2020
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. Keywords: cuprates, electron–hole dimers, pseudogap behavior, molecular field DOI: 10.1134/S1063783420090206
1. INTRODUCTION In spite of a great number of experimental and theoretical works on studying cuprates published after the discovery of high-temperature superconductivity (HTSC), the problem of the leading mechanism of HTSC and also other unusual properties of cuprates, first of all, so called “pseudogap” behavior are the subjects of hot discussions actually up to now. The pseudogap behavior in hole-doped cuprates with a characteristic temperature T * that becomes zero at critical doping pc ≈ 0.20 is one of most puzzling properties of the normal phase of HTSC cuprates [1]. Near the pseudogap at temperatures lower than T *, the thermodynamic and electron-transport properties of all cuprates are changed mainly due to suppression of low-energy electron excitations. Most of physicists consider the pseudogap phase as a precursor of the superconducting phase and a “key” to the discovery of physical principles that determine the behavior of cuprates as the Rosetta Stone of a sort that enabled linguists to decipher Egyptian hieroglyphs. In general, cuprate superconductors have several characteristic temperatures, the “main” of them is the pseudogap temperature T*; however, the magnetic susceptibility peak is observed also at higher temperatures, and the changes in the symmetry and the transport properties are observed also at lower characteristic temperatures. The analysis of the characteristic temperatures in cuprates 214 and 123 [2] shows that dependence T*(p) is only one of the famil
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