Stripes, carriers, and high-T[sub c] in the cuprates

Abstract

Abstract. Considering both "large-U " and "small-U " orbitals it is found that the high-T c cuprates are characterized by a striped structure, and three types of carriers: polaron-like "stripons" carrying charge, "quasielectrons" carrying charge and spin, and "svivons" carrying spin and lattice distortion. It is shown that this electronic structure leads to the anomalous physical properties of the cuprates, and specifically the systematic behavior of the resistivity, Hall constant, and thermoelectric power. High-T c pairing results from transitions between pair states of quasielectrons and stripons through the exchange of svivons. A pseudogap phase occurs when pairing takes place above the temperature where stripons become coherent, and this temperature determines the Uemura limit. INTRODUCTIONThe existence of static stripes in the CuO 2 planes has been observed in some superconducting cuprates [1,2], and there is growing evidence on the existence of dynamic stripes in others [3]. Many experimental observations have been pointing to the presence of both itinerant and almost localized (or polaron-like) carriers in these materials.Though one-band theoretical models have been quite popular, and easier to treat, first-principles calculations [4] indicate that such models are probably oversimplified. Here an approach is proposed to the cuprates, taking into account the existence of both "large-U" and "small-U" orbitals in the vicinity of the Fermi level (E F ). AUXILIARY PARTICLESThe large-U orbitals are treated using the "slave-fermion" method [5]. An electron of these orbitals at site i and of spin σ is then created by d † iσ = e † i s i,−σ , if it is in the "upper-Hubbard-band", and by d ′ † iσ = σs † iσ h i , if it is in a Zhang-Rice-type