FRUSTRATION OF ANTIFERROMAGNETISM IN THE T-T'-HUBBARD MODEL AT WEAK-COUPLING

The perfect-nesting instability towards antiferromagnetism of the Hubb ard model is suppressed by next-nearest neighbor hopping t'. The asymp totic behavior of the critical coupling U-c(t') at small t' is calcula ted in dimensions d = 2, 3, infinity using Hartree theory; this yields the exact result at least in d > 2. The order of the transition is al so determined. A region of stability of a metallic antiferromagnetic p hase in d = 3 is identified.