Regensburg 2013 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 30: Correlated Electrons: Quantum Impurities, Kondo Physics

TT 30.4: Talk

Tuesday, March 12, 2013, 10:15–10:30, H21

Magnetic exchange coupling mediated by Kondo singlets — •Andrej Schwabe, Irakli Titvinidze, and Michael Potthoff — University Hamburg, Hamburg, Germany

When a magnetic impurity is antiferromagnetically exchange coupled to a metallic bath its spin degree of freedom may be quenched due to the Kondo effect. For several impurities, this competes with the RKKY indirect magnetic exchange. In a finite quantum box and for a weak coupling, this competition may encounter drastic modifications due to the presence of a finite size gap [1,2].
Here we extend our previous studies to the strong-coupling regime where almost local Kondo singlets are formed. In the ideal situation of a one-dimensional nano chain and large coupling, the bath is effectively cut into several pieces, which are magnetically coupled by a new type of indirect exchange that is mediated by virtual excitations of the local Kondo singlets. We derive an effective low-energy Hamiltonian for this strong-coupling regime. Its main contributions stem from an "inverse indirect magnetic exchange" between substrate pieces connected by local Kondo singlets. Different magnetic states depending on the number and the position of the impurities are analysed and compared with numerical calculations performed with a variational matrix-product states code. These can be understood by the adiabatic connection between the weak and the strong-coupling regime.
[1] A. Schwabe, D. Gütersloh, M. Potthoff, arXiv:1208.2209 (2012)
[2] W. B. Timm, J. Kroha, J. von Delft, PRL 82, 2143 (1999)