Physical Review Letters
Phase Transitions in the Quantum Heisenberg Model
Freeman J. Dyson, Élliott H. Lieb, Barry Simon A
Abstract
We rigorously prove that in three or more dimensions, the nearest-neighbor, simple-cubic, ferromagnetic, quantum Heisenberg model of spin $S(=\frac{1}{2}, 1, \dots{})$ has a phase transition at nonzero temperature.