Kondo effects in a triangular triple quantum dot with lower symmetries

A. Oguri, S. Amaha, Y. Nishikawa, T. Numata, M. Shimamoto, A. C. Hewson, and S. Tarucha
Phys. Rev. B 83, 205304 – Published 10 May 2011

Abstract

We study the low-energy properties and characteristic Kondo energy scale of a triangular triple quantum dot, connected to two non-interacting leads, in a wide parameter range of a gate voltage and distortions which lower the symmetry of an equilateral structure, using the numerical renormalization group approach. For large Coulomb interactions, the ground states with different characters can be classified according to the plateaus of Θ(δeδo)(2/π), where δe and δo are the phase shifts for the even and odd partial waves. At these plateaus of Θ, both Θ and the occupation number Ntot(δe+δo)(2/π) take values close to integers, and thus the ground states can be characterized by these two integers. The Kondo effect with a local moment with total spin S=1 due to a Nagaoka mechanism appears on the plateau, which can be identified by Θ2.0 and Ntot4.0. For large distortions, however, the high-spin moment disappears through a singlet-triplet transition occurring within the four-electron region. It happens at a crossover to the adjacent plateaus for Θ0.0 and Θ4.0, and the two-terminal conductance has a peak in the transient regions. For weak distortions, the SU(4) Kondo effect also takes place for Ntot3.0. It appears as a sharp conductance valley between the S=1/2 Kondo ridges on both sides. We also find that the characteristic energy scale T* reflect these varieties of the Kondo effect. Particularly, T* is sensitive to the distribution of the charge and spin in the triangular triple dot.

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  • Received 10 August 2010

DOI:https://doi.org/10.1103/PhysRevB.83.205304

©2011 American Physical Society

Authors & Affiliations

A. Oguri1, S. Amaha2,3, Y. Nishikawa1, T. Numata1, M. Shimamoto1, A. C. Hewson4, and S. Tarucha5

  • 1Department of Physics, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan
  • 2Quantum Spin Information Project, ICORP-JST, Atsugi-shi, Kanagawa 243-0198, Japan
  • 3Low Temperature Physics Laboratory, RIKEN, Wako-shi, Saitama 351-0198, Japan
  • 4Department of Mathematics, Imperial College, 180 Queen’s Gate, London SW7 2BZ, UK
  • 5Department of Applied Physics, School of Engineering, University of Tokyo, Bunkyo-ku, Tokyo 133-8656, Japan

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Issue

Vol. 83, Iss. 20 — 15 May 2011

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