  Recent results on electrons and holes doped CuO 2 planes confirm 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 holes doping, antibonding
one for electrons doping). The symmetry of the superconductive gap can be
related to the Bragg scattering of electronic Bloch states near the edges of
the AF pseudogap. Assuming a standard phonon coupling, one then predicts for
commensurate AF a pure d symmetry of the superconductive gap for underdoped
samples and d symmetry plus an ip 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. The simple band approximation used here could no doubt be made more
realistic by a specific inclusion of electron correlations and by a better
description of AF short range order. Uncommensurate AF, as in LSCO, is not
considered here.
