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Ferromagnetism in the Hubbard model on the square lattice: Improved instability criterion for the Nagaoka state

P. Wurth·G. Uhrig·E. Mueller-Hartmann
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Abstract

The instability of the fully polarized ferromagnetic state (Nagaoka state) with respect to single spin flips is re-examined for the Hubbard model on the square lattice with a large family of variational wave functions which include correlation effects of the majority spins in the vicinity of the flipped spin. We find a critical hole density of $δ_{cr} = 0.251$ for $U = \infty$ and a critical coupling of $U_{cr} = 77.7 t$. Both values improve previous variational results considerably.

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P. Wurth, G. Uhrig, E. Mueller-Hartmann. 1995-12-08. Ferromagnetism in the Hubbard model on the square lattice: Improved instability criterion for the Nagaoka state. https://arxiv.org/abs/cond-mat/9512060

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