Frustration of antiferromagnetism in the t-t'-Hubbard model at weak   coupling
  The perfect-nesting instability towards antiferromagnetism of the Hubbard model is suppressed by next-nearest neighbor hopping t'. The exact asymptotic behavior of the critical coupling U_c(t') at small t' is calculated in dimensions d=2,3 and infinity using Hartree theory, and the order of the transition is determined. A region of stability of a metallic antiferromagnetic phase in d=3 is identified. 
W. Hofstetter and D. Vollhardt (Theoretische Physik III, Universitaet   Augsburg)