Numerical renormalization-group study of a Kondo hole in a one-dimensional Kondo insulator

We have studied a Kondo hole in a one-dimensional Kondo insulator at half-filling using a density matrix formulation of the numerical renormalization group. The Kondo hole introduces midgap states. The spin density introduced by the hole is localized in the vicinity of the hole. It resides primarily in the f spins for small exchange coupling J and in the conduction spins for large J. We present results on the spin gap, charge gap, and neutral gap. The presence of the Kondo hole reduces the charge gap but not the spin gap relative to a Kondo insulator without defects. For small J, the spin gap is smaller than the charge gap, while for large J, the spin gap is larger than the charge gap. RKKY interactions are reduced by the Kondo hole as can be seen in the staggered susceptibility. copyright 1996 The American Physical Society