Kondo impurity in one dimensional O(3)-invariant Superconductor

The conventional Kondo model consists of a bath of free electrons interacting with a single quantum impurity. For an antiferromagnetic impurity-bath coupling, there is only one phase where the model flows to the strong coupling fixed point characterized by many-particle dynamical screening of the impurity spin. On the other hand, the ferromagnetic coupling is an irrelevant perturbation and hence the model remains in the local moment [JP1] regime where the impurity spin remains unscreened.



We study a variant of this problem but has an interacting bath and discover using the Bethe-Ansatz that the model is richer with several more phases. For an antiferromagnetic impurity coupling, apart from the usual Kondo screening, there exists a new kind of phase where the impurity is screened by a single particle bound mode formed at the impurity site. Surprisingly, even when the coupling is ferromagnetic, the impurity can be screened – however, this screening occurs not at the ground state but in the high energy excited states.

Using the density matrix renormalization group, we compute various local observables. These behave differently in the various phases[JP2] . We show the implication of the single-particle bound mode in local measurable quantities, in unitary time evolution, and in non-local quantities like the entanglement entropy.