abstract

The free electron Kondo problem can be described by a onedimensional (1D)
model because only the swave part of the electronic wavefunction is affected
by the Kondo coupling. Since only the spin degrees of freedom are involved in
the Kondo interaction, and due to spincharge separation in 1D, the universal
low energy long distance physics of the Kondo model also arises when a magnetic
impurity is coupled to the end of a gapless antiferromagnetic J_1J_2 spin1/2
chain, where J_1(J_2) is the (next)nearest neighbor coupling. Experimental
realizations of such spin chain models are possible and using various
analytical and numerical techniques, we present a detailed and quantitative
comparison between the usual free electron Kondo model and such spin chain
versions of the Kondo problem. For the gapless J_1J_2 spin chain two cases
are studied, with zero next nearest neighbor coupling, J_2=0, and with a
critical second neighbor coupling, J_2=J_2c. We first focus on the spin chain
impurity model at J_2c~0.2412 where a bulk marginal coupling present in the
spin chain model for J_2