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 , where and are the phase shifts for the even and odd partial waves. At these plateaus of , both and the occupation number 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 due to a Nagaoka mechanism appears on the plateau, which can be identified by and . 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 and , and the two-terminal conductance has a peak in the transient regions. For weak distortions, the SU(4) Kondo effect also takes place for . It appears as a sharp conductance valley between the Kondo ridges on both sides. We also find that the characteristic energy scale reflect these varieties of the Kondo effect. Particularly, is sensitive to the distribution of the charge and spin in the triangular triple dot.
14 More- Received 10 August 2010
DOI:https://doi.org/10.1103/PhysRevB.83.205304
©2011 American Physical Society