Quantum transport through circularly coupled triple quantum dots

Abstract

We report a theoretical investigation into the Kondo transport properties ofcircularly coupled triple quantum dots (QDs), composed of one Coulomb-typeQD and two Kondo-type QDs. These two Kondo-type QDs are coupled togetherto form an Aharonov–Bohm (AB) ring by two channels: the direct couplingt0 and the indirectone t via aCoulomb-type QD-M; these respectively serve as the continuous and discrete channels for observing the Fano effect.It is particularly interesting that this QD system may be seen as a powerful platform forstudying the coexistence and interplay of Kondo, Fano and AB effects. First we study thedevice conductance in the absence of a magnetic field, and striking competition betweent0 and t is obtained. It is shown that the Kondo-induced conductance peak pattern without direct couplingis completely changed into a new pattern characteristic of one deep Fano-induced valley whent0 becomes sufficiently strong. Furthermore, we show that the position of the bottomof the Fano valley is determined only by the specific values of the direct andindirect couplings. Then by applying a magnetic field to this QD ring weexplore the AB oscillations. It is shown that the phase-locking effect still existseven in the Kondo regime, and the conductance is an even function of thereduced magnetic flux. The AB oscillation pattern becomes very complex for theQD-M level |εM|≈0 andstrong t,t0 couplings. In addition, the Fano-type valley can be strongly varied by the magnetic field inthe AB ring.