Quantum phase transition of Ising-coupled Kondo impurities

M. Garst, S. Kehrein, T. Pruschke, A. Rosch, and M. Vojta
Phys. Rev. B 69, 214413 – Published 18 June 2004

Abstract

We investigate a model of two Kondo impurities coupled via an Ising interaction. Exploiting the mapping to a generalized single-impurity Anderson model, we establish that the model has a singlet and a (pseudospin) doublet phase separated by a Kosterlitz-Thouless quantum phase transition. Based on a strong-coupling analysis and renormalization-group arguments, we show that at this transition the conductance G through the system either displays a zero-bias anomaly, GV2(21), or takes a universal value, G=(e2π)cos2(π22), depending on the experimental setup. Close to the Toulouse point of the individual Kondo impurities, the strong-coupling analysis allows us to obtain the location of the phase boundary analytically. For general model parameters, we determine the phase diagram and investigate the thermodynamics using numerical renormalization-group calculations. In the singlet phase close to the quantum phase transition, the entropy is quenched in two steps: first the two Ising-coupled spins form a magnetic minidomain which is, in a second step, screened by a Kondoesque collective resonance in an effective solitonic Fermi sea. In addition, we present a flow-equation analysis which provides a different mapping of the two-impurity model to a generalized single-impurity Anderson model in terms of fully renormalized couplings, which is applicable for the whole range of model parameters.

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  • Received 15 October 2003

DOI:https://doi.org/10.1103/PhysRevB.69.214413

©2004 American Physical Society

Authors & Affiliations

M. Garst1, S. Kehrein2, T. Pruschke2, A. Rosch1, and M. Vojta1

  • 1Institut für Theorie der Kondensierten Materie, Universität Karlsruhe, Postfach 6980, 76128 Karlsruhe, Germany
  • 2Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Universität Augsburg, 86135 Augsburg, Germany

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Vol. 69, Iss. 21 — 1 June 2004

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