Long range order in the anisotropic quantum ferromagnetic Heisenberg model
- Cite this article as:
- Kennedy, T. Commun.Math. Phys. (1985) 100: 447. doi:10.1007/BF01206139
We study the anisotropic quantum mechanical ferromagnetic Heisenberg model. By anisotropic we mean that thex andy exchange constants are equal but smaller than thez exchange constant. We show that for any amount of anisotropy there is long range order in two or more dimensions at low enough temperature. We also develop a convergent low temperature expansion and use it to prove exponential decay of the truncated correlation functions.