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Oguri A.,Osaka City University | Amaha S.,Quantum Spin Information Project | Amaha S.,RIKEN | Nishikawa Y.,Osaka City University | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

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 pašeter 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≡(δ e-δo)(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 N tot≡(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. © 2011 American Physical Society. Source

Huang S.-M.,RIKEN | Tokura Y.,Nippon Telegraph and Telephone | Akimoto H.,RIKEN | Kono K.,RIKEN | And 4 more authors.
Japanese Journal of Applied Physics | Year: 2011

The spin bottleneck effect was first observed in vertical double quantum dots with different g factors in high magnetic fields. We further investigate the spin-dependent resonance tunneling through the same quantum dot system in low magnetic fields. There are no resonance tunneling peak lines, even though one of the Zeeman levels is aligned, because the mismatch of the other Zeeman sublevels blocks the resonance tunneling. However, the level broadening effect partially releases the spin-dependent blockade. As a compromise between two effects, one resonance tunneling peak line splits into two peak lines and forms a kink structure. The split of the two current peak lines is half of Zeeman energy difference between two dots. © 2011 The Japan Society of Applied Physics. Source

Huang S.M.,RIKEN | Huang S.M.,National Chiao Tung University | Tokura Y.,Nippon Telegraph and Telephone | Akimoto H.,RIKEN | And 5 more authors.
Physical Review Letters | Year: 2010

We investigated the electron transport property of the InGaAs/GaAs double quantum dots, the electron g factors of which are different from each other. We found that in a magnetic field, the resonant tunneling is suppressed even if one of the Zeeman sublevels is aligned. This is because the other misaligned Zeeman sublevels limit the total current. A finite broadening of the misaligned sublevel partially relieves this bottleneck effect, and the maximum current is reached when interdot detuning is half the Zeeman energy difference. © 2010 The American Physical Society. Source

Tokura Y.,Nippon Telegraph and Telephone | Kubo T.,Quantum Spin Information Project | Shin Y.-S.,Quantum Spin Information Project | Ono K.,Quantum Spin Information Project | And 3 more authors.
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2010

We theoretically investigated the resonant current that passes through a series coupled double quantum dots (QDs) subject to different Zeeman splittings under finite bias and strong Coulomb interaction conditions. When the Zeeman fields are different but collinear, there is always a single resonant peak. And when both Zeeman sub-levels of the QD near the source reservoir (probe QD) can be filled, we can expect the current to be strongly suppressed, which can be identified as a spin blockade. When the magnetic fields in each QD are non-collinear, we need to consider three parameters, the Zeeman energy in the probe (sample) dot, BZp (BZs) and the relative angle of these fields, θ. If the effect of the Coulomb interaction can be neglected, we can expect to observe four resonant peaks when BZp ≠ BZs since the spin eigenstate in one QD has a finite tunnel matrix element with both spin eigenstates in the other QD. However, the Coulomb correlation modifies the result significantly. When BZp > BZs, we always found a single resonant peak as a function of the energy offset. The peak current is maximum when θ = 0 and decreases monotonically for a larger θ < π / 2. In contrast, when BZp < BZs, there were three peaks for θ < π / 4 and two peaks for θ > π / 4. © 2009 Elsevier B.V. All rights reserved. Source

Amaha S.,Quantum Spin Information Project | Hatano T.,Quantum Spin Information Project | Tamura H.,Nippon Telegraph and Telephone | Kubo T.,Quantum Spin Information Project | And 6 more authors.
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2010

Three laterally coupled vertical single quantum dots (tQDs) in a collinear arrangement, with common source and drain electrodes, are investigated. The tQDs are formed inside three connected pillars (mesa1, mesa2, mesa3) with four side gate electrodes (G1, G2 (G2'), G3). Three families of Coulomb oscillation lines corresponding to charges in the numbers of electrons in the three dots are observed, and the few-electron charge configurations can be assigned. We also discuss the separation of adjacent Coulomb peak lines in the stability diagram, indicating that the inter-dot Coulomb energy between adjacent dots (mesa1-mesa2 and mesa2-mesa3) is significantly larger than that between the two non-adjacent dots (mesa1-mesa3). © 2009 Elsevier B.V. All rights reserved. Source

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