Neel order, ring exchange and charge fluctuations in the half-filled Hubbard model

Details Neel order, ring exchange and charge fluctuations in the half-filled Hubbard model Neel order, ring exchange and charge fluctuations in the half-filled Hubbard model

2004-12-01

arxiv.org/abs/cond-mat/0412033v3

Phys. Rev. B 72, 115114 (2005)

Physics

Condensed Matter

Strongly Correlated Electrons

9 pages - 3 figures - References and details to help the reader added

Scientific paper

10.1103/PhysRevB.72.115114

We investigate the ground state properties of the two dimensional half-filled one band Hubbard model in the strong (large-U) to intermediate coupling limit ({\it i.e.} away from the strict Heisenberg limit) using an effective spin-only low-energy theory that includes nearest-neighbor exchange, ring exchange, and all other spin interactions to order t(t/U)^3. We show that the operator for the staggered magnetization, transformed for use in the effective theory, differs from that for the order parameter of the spin model by a renormalization factor accounting for the increased charge fluctuations as t/U is increased from the t/U -> 0 Heisenberg limit. These charge fluctuations lead to an increase of the quantum fluctuations over and above those for an S=1/2 antiferromagnet. The renormalization factor ensures that the zero temperature staggered moment for the Hubbard model is a monotonously decreasing function of t/U, despite the fact that the moment of the spin Hamiltonien, which depends on transverse spin fluctuations only, in an increasing function of t/U. We also comment on quantitative aspects of the t/U and 1/S expansions.

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