On the Fermi surface geometry and antiferromagnetism of YBa2Cu3O6+x

We argue that, for a square lattice and a nearly half-full band, the random -phase approximation (RPA) in general tends to give an instability towards antiferromagnetism with q(AF) = (pi,pi)/a, regardless of whether the Fermi surface (FS) is nested or not for this wave vector. Specifically, for a one -band model of YBa2Cu3O6+x, with its well-known nearly square, [10]-oriente d FS, we find the real part of the Lindhard susceptibility to have a broad maximum at q(AF) for electron and hole-dopings up to about 10%. This hither to overlooked result has implications for current electronic models of high -temperature superconductivity. (C) 2000 Elsevier Science B.V. All rights r eserved.