Validity of the spin-wave approximation for the free energy of the Heisenberg ferromagnet
Correggi, Michele
Giuliani, Alessandro
Seiringer, Robert
We consider the quantum ferromagnetic Heisenberg model in three dimensions, for all spins S ≥ 1/2. We rigorously prove the validity of the spin-wave approximation for the excitation spectrum, at the level of the first non-trivial contribution to the free energy at low temperatures. Our proof comes with explicit, constructive upper and lower bounds on the error term. It uses in an essential way the bosonic formulation of the model in terms of the Holstein-Primakoff representation. In this language, the model describes interacting bosons with a hard-core on-site repulsion and a nearest-neighbor attraction. This attractive interaction makes the lower bound on the free energy particularly tricky: the key idea there is to prove a differential inequality for the two-particle density, which is thereby shown to be smaller than the probability density of a suitably weighted two-particle random process on the lattice.
Springer
2015
info:eu-repo/semantics/article
doc-type:article
text
http://purl.org/coar/resource_type/c_6501
https://research-explorer.app.ist.ac.at/record/1572
Correggi M, Giuliani A, Seiringer R. Validity of the spin-wave approximation for the free energy of the Heisenberg ferromagnet. <i>Communications in Mathematical Physics</i>. 2015;339(1):279-307. doi:<a href="https://doi.org/10.1007/s00220-015-2402-0">10.1007/s00220-015-2402-0</a>
eng
info:eu-repo/semantics/altIdentifier/doi/10.1007/s00220-015-2402-0
info:eu-repo/semantics/openAccess