Edge states in antiferromagnetic quantum spin chains

The structure of edge states in general finite antiferromagnetic quantum spin chains with arbitrary spin value S is discussed within the framework of the nonlinear-sigma model (NLσM) plus a topological θ term. Based on a large-N theory of SU(N) quantum antiferromagnets and strong-coupling expansion, we argue that edge states with fractionalized spin quantum number S’ exist in all spin chains with S≥1, with S’=S/2 for integer spin chains and S’=(S-1/2)/2 for half-integer spin chains.