What are spin currents in Heisenberg magnets?
arXiv:cond-mat/0405312 · doi:10.1140/epjb/e2004-00348-9
Abstract
We discuss the proper definition of the spin current operator in Heisenberg magnets subject to inhomogeneous magnetic fields. We argue that only the component of the naive "current operator" J_ij S_i x S_j in the plane spanned by the local order parameters <S_i> and <S_j> is related to real transport of magnetization. Within a mean field approximation or in the classical ground state the spin current therefore vanishes. Thus, finite spin currents are a direct manifestation of quantum correlations in the system.
4 pages, 1 figure, published version