Matthias Vojta, Ralf Bulla, Walter Hofstetter
Published 2001-06-22, updated 2002-04-04Version 2
We discuss models of interacting magnetic impurities coupled to a metallic host. If twice the sum of the impurity spins is larger than the total number of host screening channels, the system shows one or more quantum phase transitions where the ground-state spin changes as a function of the inter-impurity couplings. The simplest example is realized by two spin-1/2 Kondo impurities coupled to a single orbital of the host; this model exhibits a singlet-doublet transition. We investigate the phase diagram and crossover behavior of this model and present Numerical Renormalization Group results together with general arguments showing that the quantum phase transition is either of first order or of the Kosterlitz-Thouless type, depending on the symmetry of the Kondo couplings. Connections to other models and possible applications are discussed.
Comments: 4 pages, 3 figs. (v2) Minor changes and clarifications, small asymmetry case discussed; application to multilevel quantum dots emphasized, in particular to the experiment of W. G. van der Wiel et al., cond-mat/0110432, where indications for a Kosterlitz-Thouless-type transition in a multilevel dot are found. Final version as published
Journal: Phys. Rev. B 65, 140405(R) (2002)
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