Low-lying properties in a decorated Heisenberg spin chain

A decorated quantum spin chain is introduced, which realizes the strong coupling limit of a generalized Kondo lattice model at half-filling. The low-lying properties of the decorated spin system are discussed. In the continuum and semiclassical limit of the present model, the nonlinear sigma model with a topological term is derived and the conjecture for the low-lying state is proposed. Validity of the conjecture seems to be supported by the perturbational expansions and by the density matrix renormalization group calculations.