Kondo effects in a triangular triple quantum dot: Numerical renormalization group study in the whole region of the electron filling
Kondo effects in a triangular triple quantum dot: Numerical renormalization group study in the whole region of the electron filling
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DOI：
10.1103/physrevb.80.155330
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发表时间：
2009-05
影响因子：
3.7
通讯作者：
T. Numata;Y. Nisikawa;A. Oguri;A. Hewson
中科院分区：
文献类型：
--
作者：
T. Numata;Y. Nisikawa;A. Oguri;A. Hewson
利用数值重整化群（NRG）研究了宽参数范围内连接到两个非相互作用引线的三角形三重量子点的低能性质。各种近藤效应发生在这个系统取决于电子填充${N}_{\text{tot}}$，或三点的水平位置${ϵ}_{d}$。在半填充的情况下（${N}_{\text{tot}}\ensuremath{\simeq}3.0$），在串联电导的下降处，出现了SU(4) Kondo行为，并导致三角形中奇偶轨道之间的电荷重新分布。我们一般证明了准粒子在局域费米-液体基态激发时，在双端电导的零点处获得通道对称，在这种情况下，系统具有时间反转和反转对称性。它导致低能的SU(4)行为，而三角中的轨道简并决定了高能行为。在四电子填充${N}_{\text{tot}}\ensuremath{\simeq}4.0$时，由于长冈铁磁机制，局部$S=1$力矩在高温下出现。它被来自两个导电通道的电子通过两阶段近藤效应完全屏蔽，这是由奇偶轨道上电荷分布的差异引起的。
We study the low-energy properties of a triangular triple quantum dot connected to two noninteracting 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 ${N}_{\text{tot}}$, or the level position ${ϵ}_{d}$ of the triple dot. The SU(4) Kondo behavior is seen in the half-filled case ${N}_{\text{tot}}\ensuremath{\simeq}3.0$ 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 quasiparticle 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 ${N}_{\text{tot}}\ensuremath{\simeq}4.0$, 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.