Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 30: Correlated Electrons: Quantum Impurities, Kondo Physics

TT 30.10: Talk

Tuesday, March 12, 2013, 12:00–12:15, H21

Inverse indirect magnetic exchange in one and higher dimensions — •Irakli Titvinidze, Andrej Schwabe, Anke Braun, and Michael Potthoff — I. Institut für Theoretische Physik, Universität Hamburg, Jungiusstraße 9, 20355 Hamburg, Deutschland

It is well known that magnetic adatoms on a metallic substrate surface experience the Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect magnetic exchange. Here we consider the limit of a strong antiferromagnetic Kondo coupling J which for certain geometries can lead to a quantum confinement of conduction electrons and the formation of local magnetic moments at substrate sites. It is argued that these local moments may couple magnetically via almost completely localized Kondo singlets that are formed for strong J. This novel inverse indirect magnetic exchange (IIME) is investigated numerically by means of the density-matrix renormalization group for one-dimensional multi-impurity Kondo models and for diluted Kondo lattices with “adatoms” present at every second “substrate” site. For the latter, our calculations show that as a function of J there is a crossover from ferromagnetic order driven by the RKKY interaction at weak J to ferromagnetism induced by the IIME interaction for strong J. We find excellent agreement with the results of corresponding calculations obtained by real-space dynamical mean-field theory (R-DMFT). R-DMFT is then used to study different adatom nanostructures on top of a two-dimensional substrate. We analyze the conditions under which the IIME interaction and ferromagnetic order induced by IIME also persists in two- and higher-dimensional systems.