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This paper deals with well-known notion of PF-rings, that is, rings in which principal ideals are flat. We give a new characterization of PF-rings. Also, we provide a necessary and sufficient conditio...
Let R be a noetherian commutative ring, and F : · · · → F2 → F1 → F0 → 0 a complex of flat R-modules. We prove that if (p) ⊗R F is acyclic for every p ∈ SpecR, then F is acyclic, and H0(F) is R...
Estimating the Hubbard repulsion sufficient for the onset of nearly-flat-band ferromagnetism
Hubbard repulsion sufficient onset of nearly-flat-band ferromagnetism
2011/3/2
We consider nearly-flat-band Hubbard models of a ferromagnet, that is the models that are weak perturbations of those flat-band Hubbard models whose ground state is ferromagnetic for any nonzero stren...