arXiv:1602.00155
Low-Temperature Spin-Wave Approximation for the Heisenberg Ferromagnet
Michele Correggi, Alessandro Giuliani, Robert Seiringer
Abstract
We study the low temperature thermodynamics of the quantum Heisenberg ferromagnet in three dimension for any value of the spin $ S \geq 1/2 $. We report on a rigorous proof of the validity of the spin-wave approximation for the excitation spectrum, at the level of the first non-trivial contribution to the free energy as the inverse temperature $ β\to \infty $.