Low-Density Ferromagnetism in the Hubbard Model
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Abstract
We study analytically the stability of the saturated ferromagnetic ground state (the Nagaoka state) of the Hubbard model in the low electron density limit with the mean-field approach. We find that the critical Uc is just 4πt, where t is the hopping integral between the nearest neighbours, i.e., when U is larger than 4πt,the paramagnetic state is unstable with respect to the ferromagnetic state, and vice versa.
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