Interaction of a Magnetic Impurity with Strongly Correlated Conduction Electrons

TL;DR

This paper investigates how a magnetic impurity interacts with strongly correlated conduction electrons described by a Hubbard model, revealing modifications to the Kondo effect and impurity behavior under different doping conditions.

Contribution

It derives an effective Hamiltonian for a magnetic impurity in a strongly correlated electron system, extending the Kondo model to include correlation effects and doping-dependent interactions.

Findings

Impurity attracts holes in hole-doped systems.

Strong correlations modify the exchange coupling of the impurity.

Doping influences the magnetic and charge interactions around the impurity.

Abstract

We consider a magnetic impurity which interacts by hybridization with a system of strongly correlated conduction electrons. The latter are described by a Hubbard Hamiltonian. By means of a canconical transformation the charge degrees of freedom of the magnetic impurity are eliminated. The resulting effective Hamiltonian $H_{\rm eff}$ is investigated and various limiting cases are considered. If the Hubbard interaction $U$ between the conduction electrons is neglected $H_{\rm eff}$ reduces to a form obtained by the Schrieffer-Wolff transformation, which is essentially the Kondo Hamiltonian. If $U$ is large and the correlations are strong $H_{\rm eff}$ is changed. One modification concerns the coefficient of the dominant exchange coupling of the magnetic impurity with the nearest lattice site. When the system is hole doped, there is also an antiferromagnetic coupling to the nearest neighbors of that site involving additionally a hole. Furthermore, it is found that the magnetic impurity attracts a hole. In the case of electron doping, double occupancies are repelled by the impurity. In contrast to the hole-doped case, we find no magnetic coupling which additionally involves a doubly occupied site.