title: Ferromagnetic Lieb-Mattis theorem.
abstract: We prove ferromagnetic ordering of energy levels for XXX Heisenberg chains with spins of arbitrary magnitude, thus extending our previous result for the spin-1/2 chain. Ferromagnetic ordering means that the minimum energies in the invariant subspaces of fixed total spin are monotone decreasing as a function of the total spin. This result provides a ferromagnetic analogue of the well-known theorem by Lieb and Mattis about ordering of energy levels in antiferromagnetic and ferrimagnetic systems on bipartite graphs.
authors.affiliation: Department of Mathematics, University of California at Davis, Davis, California 95616, USA. bxn@math.ucdavis.edu
authors.forename: Bruno
authors.initials: B
authors.lastname: Nachtergaele
authors.forename: Shannon
authors.initials: S
authors.lastname: Starr