Numerical renormalization group study of the one-dimensional Kondo insulator

We have studied the one-dimensional Kondo chain at half filling using a density matrix formulation of the numerical renormalization group. The charge gap is larger than the spin gap for all antiferromagnetic values of the exhange coupling J. A new type of excitation, a neutral spin singlet, consists of a particle and a hole which are repulsive for J≳5t and attractive for J≲5t. As J→0, RKKY interactions become more important and the staggered susceptibility χ(q=2${\mathit{k}}_{\mathit{F}}$) diverges. We have also studied χ(q) and the dispersion of the low-lying spin excitations as a function of wave vector q.