Regensburg 2016 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 16: Transport: Quantum Dots, Quantum Wires, Point Contacts

TT 16.1: Vortrag

Montag, 7. März 2016, 15:00–15:15, H21

Suppression and break-down of Kondo screening in asymmetric double-quantum-dot systems — •Ammar Nejati, Katinka Ballmann, and Johann Kroha — Physikalisches Institut and Bethe Center for Theoretical Physics, Universität Bonn, Germany

Due to recent advances in semiconductor device technology, it is possible to investigate the Kondo effect in presence of magnetic correlations with fully-controllable double-quantum-dot (qdot) systems. Here we present a renormalization group (RG) method which can describe the different regimes observed in a highly-tunable semiconductor device with 2 qdots coupled to 3 leads ; especially, the principal observation which was the formation of a Kondo state for one qdot along with suppression of the Kondo resonance in the other, in presence of RKKY exchange interaction. The RG method is developed to consider local spin screening in multi-impurity Kondo systems in presence of magnetic fluctuations due to the carrier-mediated RKKY interaction. We calculate the beta-function for the Kondo coupling J between a localized spin (of the impurity/qdot) and conduction electrons in 1-loop order, taking into account that J is modified by the RKKY coupling to the neighbouring impurities/qdots. This leads to a suppression of T_K as a function of the dimensionless RKKY coupling parameter y, and ultimately, break-down of Kondo screening at a maximal RKKY coupling y_max which depends on the bare parametres only. In the 2-impurity case, the dependence of the renormalized Kondo temperature of each dot is drastically different if there is an asymmetry in the bare Kondo couplings.