Eur. Phys. J. B 30, 427-435 (2002)
https://doi.org/10.1140/epjb/e2002-00399-x

On the nature of antiferromagnetism in the CuO₂ planes of oxide superconductors

¹ Laboratoire de Physique des Solides (associé au CNRS) , and Université Paris-Sud, bâtiment 510, 91405 Orsay, France
² Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan

Received: 22 March 2002
Revised: 20 August 2002
Published online: 31 December 2002

Abstract

Recent results regarding electron- and hole-doped CuO₂ planes can be rather easily explained by the marked covalency of CuO bonding, suggesting a band picture of long and short range antiferromagnetism. The maxima of superconductive T_c versus doping can be related to the crossing by the Fermi level of the edges of the pseudogap due to antiferromagnetic short range order (bonding edge for hole-doping, antibonding for electron-doping). The symmetry of the superconductive gap can be related to the Bragg scattering of electronic Bloch states near the edges of the antiferromagnetism (AF) pseudogap. Assuming a standard phonon coupling, one then predicts for commensurate AF a pure symmetry for the superconductive gap for underdoped samples and symmetry plus an imaginary contribution of s or d_xy symmetry contribution increasing linearly with overdoping. This seems in agreement with recent measurements of gap symmetry for YBCO, but should be more fully tested, especially for electron-doped samples. Incommensurate AF, as in LSCO, is not considered here. The simple Hartree-Fock band approximation used could no doubt be made more realistic by specific inclusion of electron correlations and by a better description of the AF short range order. This weak atomic repulsion U model, standard in transitional metals, is complementary to the strong U models usually assumed in oxides. It considers specifically the possible effects, in doped samples, of a short range AF which could be slowly dynamical or static, possibly including in that case recent evidences of nanostructures of two different phases.