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 RKKYlike two-spin model ("RKKY from IIME") or within an effective central-spin model, depending on edge-spin distance and system size.

Crossover from conventional to inverse indirect magnetic exchange in the depleted Anderson lattice

“…The depleted Anderson lattice model has been considered beforehand to study fundamental questions of magnetic coupling mechanisms 9,10 and to describe artificial Kondo systems realized as ultracold atoms trapped in optical lattices. 14 It is related to two-dimensional superlattices consisting of periodic arrangements of f -electronand non-interacting layers 45 and may be used to describe systems of magnetic atoms on non-magnetic metallic surfaces where a manipulation of the adatom geometry and a precise mapping of magnetic couplings is accessible to scanning-tunneling techniques on an atomic scale. [17][18][19][20][21] We have employed two different types of mean-field approaches: (i) static mean-field theory of the effective low-energy model that emerges at strong couplings V within fourth-order perturbation theory, and (ii) dynamical mean-field theory of the full model using continuoustime quantum Monte-Carlo as impurity solver.…”