We solve analytically the NXN square lattice Hubbard model for even N at half-filling and weak coupling by a new approach. The exact ground-state wave function provides an intriguing and appealing picture of the antiferromagnetic order. Like at strong coupling, the ground state has total momentum K-tot, = (0, 0) and transforms as an s wave for even N/2 and as a d wave otherwise. (C) 2001 Elsevier Science Ltd. All rights reserved. References: 8
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