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 exchange coupling J. A new type of excitation, a neutral spin singlet, consists of a particle and a hole which are repulsive for J greater than or similar to 5t and attractive for J less than or similar to 5t. As J --> 0, RKKY interactions become more important and the staggered susceptibility chi(q = 2k(F)) diverges. We have also studied chi(q) and the dispersion of the low-lying spin excitations as a function of wave vector q.