A 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. 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. The presence of the Kondo hole reduces RKKY interactions as can be seen in the staggered susceptibility. 
Clare C. Yu