Heisenbergstr. 1, Max-Planck-Institut für Festkörperforschung, D-70569, Stuttgart, Germany

We argue that, for a square lattice and a nearly half-full band, the RPA (RPA) in general tends to give an instability towards antiferromagnetism with q_AF = (p,p)/a, regardless of whether the Fermi surface (FS) is nested or not for this wave vector. Specifically, for a one-band model of YBa₂Cu₃O_6+x, with its well-known nearly square, [10]-oriented FS, we find the real part of the Lindhard susceptibility to have a broad max. at q_AF for electron and hole-dopings up to about 10%. This hitherto overlooked result has implications for current electronic models of high-temp. supercond.
 

Physica C, 336 157-161, 2000.

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