A Real Space Glue for Cuprate Superconductors

TL;DR

This paper proposes that real space Coulomb interactions, rather than k-space dynamic screening, serve as the pairing mechanism in cuprate superconductors, explaining various experimental observations and doping-dependent phenomena.

Contribution

It introduces a real space Coulomb confinement mechanism for electron pairing in cuprates, predicting pairing symmetries and explaining charge order and doping effects.

Findings

Localized electron pairs form within CuO plaquettes due to Coulomb confinement.

Predicted d-wave pairing in hole-doped and mixed symmetry in electron-doped cuprates.

Analytical phase diagram and explanation of magic doping fractions in LSCO.

Abstract

In a recent article [Science 317, 1705 (2007)], Anderson pointed out that many theories about electron pairing in cuprate superconductors may be on the wrong track and there is no reason to believe that the dynamic screening (k-space) can provide a valid glue to hold the electron pairs together. On the other hand, the most recent experimental observations imply the possible generic existence of the real space localized Cooper pairs in amorphous insulating and other nonsuperconducting systems [M. D. Stewart Jr. et al., Science 318, 1273 (2007)]. It is therefore clear that the glue for high-T_{c} superconductors is relevant to the real space correlations. In this paper, we argue that real space electron-electron interactions can play the role of glue in high-T_{c} superconductors. It is found that two localized electrons, due to a real space Coulomb confinement effect, can be in pairing inside a single plaquette of the CuO plane. The scenario suggests appearance of a dominating d-wave-like pairing symmetry in the hole-doped cuprates, while a more complex mixed (s+d) symmetry in the electron-doped cuprates. Based on the mechanism, the relationships between the superconductivity and the charge-stripe order are discussed. In the La_{2-x}Sr_{x}CuO_{4} (LSCO) with 1/18\leq x\leq 1/4, we show that the paired electrons can self-organize into the dimerized Wigner crystal. Two kinds of quasi-one-dimensional metallic magnetic-charge stripes, where the superconductivity and dynamical spin density wave (SDW) coexist, are analytically determined. Furthermore, the physical original of the magic doping fractions (at x=1/4, 1/8, 1/9, 1/16 and 1/18) of superconductivity and an analytical phase diagram for LSCO are given.