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Boundary and finite-size effects in the competition between indirect magnetic exchange and Kondo screening

A system of conduction electrons can mediate an indirect magnetic exchange between magnetic impurites. The nonlocal exchange typically competes with the local Kondo screening of the impurity magnetic moments. In case of magnetic adatoms on non-magnetic surfaces this competition is expected to be affected by different confinement effects. Here we study this situation in the regime of intermediate hybridization strengths by means of real-space dynamical mean-field theory for a one-dimensional two-impurity Anderson model. Depending on the presence of a boundary and depending on the system size, a crossover between nonlocal and local singlet formation is observed in corresponding magnetic susceptibilities. The crossover is driven by the strong sensitivity of the Kondo temperature on the local density of states.