Heisenberg chain, anisotropic

Models have become separate research areas in statistical and solid-state physics. In addition to Hubbard models, familiar examples are two-level models, impurity models, and networks of spins in one, two, or three dimensions with isotropic, anisotropic, or frustrated interactions. Exact results for Hubbard chains with uniform t and for 5 = 1/2 Heisenberg chains with uniform exchange J are based on the Bethe ansatz, while exact results for two-dimensional Ising lattices come from transfer matrix techniques. Exact results for extended... 

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