Kondo effects in a triangular triple quantum dot: NRG study in the whole region of the electron filling

Details Kondo effects in a triangular triple quantum dot: NRG study in the whole region of the electron filling Kondo effects in a triangular triple quantum dot: NRG study in the whole region of the electron filling

2009-05-20

arxiv.org/abs/0905.3343v2

Phys. Rev. B 80, 155330 (2009)

Physics

Condensed Matter

Mesoscale and Nanoscale Physics

18 pages, 16 figures, one new section VI is added

Scientific paper

We study the low-energy properties of a triangular triple quantum dot connected to two non-interacting leads in a wide parameter range, using the numerical renormalization group (NRG). Various kinds of Kondo effects take place in this system depending on the electron filling N_{tot}, or the level position $\epsilon_d$ of the triple dot. The SU(4) Kondo behavior is seen in the half-filled case N_{tot} = 3.0 at the dip of the series conductance, and it causes a charge redistribution between the even and odd orbitals in the triangle. We show generally that the quasi-particle excitations from a local Fermi-liquid ground state acquire a channel symmetry at zero points of the two-terminal conductance, in the case the system has time-reversal and inversion symmetries. It causes the SU(4) behavior at low energies, while the orbital degeneracy in the triangle determines the high-energy behavior. At four-electron filling N_{tot} = 4.0, a local S=1 moment emerges at high temperatures due to a Nagaoka ferromagnetic mechanism. It is fully screened by the electrons from the two conducting channels via a two-stage Kondo effect, which is caused by a difference in the charge distribution in the even and odd orbitals.

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