# Berlin 2015 – wissenschaftliches Programm

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# TT: Fachverband Tiefe Temperaturen

## TT 71: Correlated Electrons: Poster Session

### TT 71.13: Poster

### Mittwoch, 18. März 2015, 15:00–18:00, Poster B

**Multi-spin multi-channel Kondo box problem** — •Mirek Hänsel, Andrej Schwabe, and Michael Potthoff — Institut für Theoretische Physik, Universität Hamburg

In a quantum box, where one or several quantum spins are coupled by a weak antiferromagnetic local exchange J to a system of non-interacting conduction electrons, the standard Kondo effect is cut by the finite system size. The residual finite-size Kondo effect can be described by perturbation theory in J. We show that the effective low-energy physics is given by a central-spin model where typically each impurity spin couples to the spin of a completely delocalized conduction-electron eigenstate at the Fermi edge. Different screening channels are given for the case of orthogonal eigenstates. We discuss the general case of several spins and several channels by analyzing various geometries, e.g., one-dimensional chains and two-dimensional lattices with different boundary conditions, and different geometrical setups of the impurity spins. The couplings in the effective central-spin model and the resulting magnetic structure are calculated as functions of the conduction-electron density and the geometry.