The bilinear–biquadratic model on the complete graph
Dávid Jakab, Gergely Szirmai, Zoltán Zimborás
Abstract We study the spin-1 bilinear–biquadratic model on the complete graph of N sites, i.e. when each spin is interacting with every other spin with the same strength. Because of its complete permutation invariance, this Hamiltonian can be rewritten as the linear combination of the quadratic Casimir operators of s u (3) and s u (2). Using group representation theory, we explicitly diagonalize the Hamiltonian and map out the ground-state phase diagram of the model. Furthermore, the complete energy spectrum, with degeneracies, is obtained analytically for any number of sites.
arXiv:1709.06602•Journal of Physics A Mathematical and Theoretical•Jan 19, 2018•9 citations