Dresden 2014 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 79: Correlated Electrons - Poster Session

TT 79.24: Poster

Mittwoch, 2. April 2014, 15:00–19:00, P2

Multi-Fermi Points in the Kondo-vs.-RKKY Quantum Box — •Mirek Hänsel, Andrej Schwabe, and Michael Potthoff — I. Institut für Theoretische Physik, Universität Hamburg, Germany

The competition between the Kondo effect and the indirect (RKKY) magnetic exchange is studied for nanoscale systems where, besides the Kondo temperature and the RKKY coupling, the finite-size gap represents a third relevant energy scale.

As has been shown recently [1] for the typical “on resonance” case with a single electron at the non-degenerate Fermi level, a Kondo-type screening of an impurity spin is possible, depending on the system’s geometry. This leads to an unconventional Kondo-vs.-RKKY competition with a re-entrant behavior that manifests itself in an unusual J dependence of spin correlations and a total ground-state spin deviating from the predictions of standard RKKY theory.

Here, we extend our studies by applying the density-matrix renormalization group as well as weak-coupling perturbation theory to multi-impurity Kondo models on confined one- and two-dimensional lattices where the conduction-electron system has a degenerate Fermi level. In this case and for weak J, the system is perturbatively mapped onto an effective central-spin model where typically each impurity spin couples to a different itinerant spin in the central region. We discuss the geometry dependence of the effective couplings and the resulting magnetic structure.
A. Schwabe, D. Gütersloh and M. Potthoff, Phys. Rev. Lett. 109, 257202 (2012).