Absence of a Magnetic Field Induced Metal-Insulator Transition in Kondo Insulators

We investigate whether or not Kondo insulators undergo a magnetic field induced metal-insulator transition in one dimension at half filling using both a density matrix formulation of the numerical renormalization group and a new analytical approach. Contrary to expectations, the quasiparticle gap never vanishes at any field and no metal-insulator transition is found. We discuss generalizing our result to three dimensions and to the asymmetric Anderson lattice. Our result is consistent with recent experiments.