Strongly Correlated Effects in a Triangular Dot System Induced by Inter-Dot Hopping and Coulomb Repulsion

Abstract

We study the transport property and the phase transition for a triple quantum dot system in a triangular geometry with one centered dot and two side dots by adopting the Wilson’s numerical renormalization group method. When three dots are decoupled with no coupling, the Kondo peak turns to reach the unitary limit, and the spin-1/2 Kondo effect is found. When the hopping between the centered dot and two side dots increases, two side dots form a local spin triplet due to the Ruderman–Kittel–Kasuya–Yosida interaction mediated by the centered dot, and the Kondo peak is suppressed. As the hopping between two side dots increases, a first order quantum phase transition occurs. In this case, two side dots form a spin singlet and the Kondo peak is recovered. When the inter-dot Coulomb repulsion between two side dots is taken into account and the hopping between two side dots is small, the charge on each side dot drops to 0.5 through a first-order quantum phase transition. As a result, one of the side dots is singly occupied, while the other one is empty. The linear conductance is suppressed due to the strong coupling between the centered dot and the singly occupied side dot. When the hopping between two side dots is large enough, the charge on each side dot decreases to 0.5 continuously and a crossover is found, for in this case the symmetry of spin configurations within two side dots is broken.