Cooperation of different exchange mechanisms in confined magnetic systems

Abstract

The diluted Kondo lattice model is investigated at strong antiferromagnetic local exchange couplings J, where almost local Kondo clouds drastically restrict the motion of conduction electrons, giving rise to the possibility of quantum localization of conduction electrons for certain geometries of impurity spins. This localization may lead to the formation of local magnetic moments in the conduction-electron system, and the inverse indirect magnetic exchange (IIME), provided by virtual excitations of the Kondo singlets, couples those local moments to the remaining electrons. Exemplarily, we study the one-dimensional two-impurity Kondo model with impurity spins near the chain ends, which supports the formation of conduction-electron magnetic moments at the edges of the chain for sufficiently strong J. Employing degenerate perturbation theory as well as analyzing spin gaps numerically by means of the density-matrix renormalization group, it is shown that the low-energy physics of the model can be well captured within an effective antiferromagnetic RKKY-like two-spin model ("RKKY from IIME") or within an effective central-spin model, depending on edge-spin distance and system size.