Kondo effect in a one-electron double quantum dot: Oscillations of the Kondo current in a weak magnetic field

Abstract

We present transport measurements of the Kondo effect in a double quantum dot charged with only one or two electrons, respectively. For the one electron case we observe a surprising quasiperiodic oscillation of the Kondo conductance as a function of a small perpendicular magnetic field |B ⊥ | 50 mT. We discuss possible explanations of this effect and interpret it by means of a fine tuning of the energy mismatch of the single dot levels of the two quantum dots. The observed degree of control implies important consequences for applications in quantum information processing. PACS numbers: 72.15.Qm, 73.21.La 73.23.Hk,The Kondo effect describes a bound state formed by interactions between a localized magnetic impurity and itinerant conduction band electrons shielding the localized spin. This results in an increased density of localized states at the Fermi energy, causing anomalous low temperature properties. In case of a degenerate ground state of a quantum dot (QD), the Kondo effect manifests itself as an enhanced conductance within the Coulomb blockade region [1,2,3]. This was first observed on large QDs with half integer spin [4,5], and later, for a total spin of S = 1, where the triplet states of a QD are degenerate [6,7,8]. On a double quantum dot (DQD) a two-impurity Kondo effect was studied [9].In this article we present the results of Kondo effect differential conductance (KDC) measurements on a DQD charged with one or two electrons in a perpendicular magnetic field B ⊥ . For only one electron (N = 1) in the DQD we observe a quasi-periodic structure of the KDC with a characteristic scale of B 0 ∼ 10 mT. In contrast for N = 2 the KDC is found to be a monotonic function of B ⊥ . We discuss possible explanations for this effect that imply consequences in quantum information processing.Our sample is fabricated from an AlGaAs/GaAs heterostructure. It embeds a two-dimensional electron system (2DES) with carrier density n s ≃ 1.8 × 10 15 m −2 and electron mobility µ ≃ 75 m 2 /Vs (at T = 4.2 K) 120 nm below its surface. Figure 1(b) shows Ti/Au-gates created by electron beam lithography. They are used to locally deplete the 2DES to define a one electron QD. The gate design is optimized for transport measurements through a QD charged by only few electrons [10]. By decreasing the voltages applied to gates g C and g X (with respect to the 2DES) while increasing the voltages on the side gates g L and g R we deform the QD into a DQD (sketched in Fig. 1(b)) [11,12]. The DQD is tuned to the regime of strong coupling to the leads and an order of magnitude stronger interdot tunnel coupling of 2t 0 ≃ 240 µeV between the adjacent QDs [11]. Measurements are performed in a dilution refrigerator at an electron temperature T 2DES ∼ 0.1 K.A nearby quantum point contact (QPC) is used to detect the charge distribution of the DQD shown in the stability diagram in Fig. 1(a) [13]. It displays a lock-in measurement of the differential transconductance G QPC = dI QPC /dU gL as a function of the dc voltages applied to gates g L and g R . In t...

Realization of theSU(N)Kondo Effect in a Strong Magnetic Field

“…The systems that we suggest contain QDs with strong Coulomb interactions between them but very small tunneling between different dots (smaller than T K ). Double QDs systems fulfilling even stricter conditions already exist [19][20][21][22] with good control over the couplings to the leads, the gate voltages, and with practically zero tunneling between the dots. The implementation of KE due to the Coulomb interactions in those systems was demonstrated [19,21,22].…”

“…Double QDs systems fulfilling even stricter conditions already exist [19][20][21][22] with good control over the couplings to the leads, the gate voltages, and with practically zero tunneling between the dots. The implementation of KE due to the Coulomb interactions in those systems was demonstrated [19,21,22]. Promising triple QDs systems are also experimentally available [23,24] making the current proposed realization of SU(3) Kondo physics reasonably possible.…”

Dynamical symmetries and quantum transport through nanostructures

“…We discussed the quantum transport through the Single Electron Transistor, molecular electronic devices and nanoelectromechanical shuttles. Many interesting properties, like thermoelectric transport through few-electron quantum dots [52] or magnetic control on the Kondo oscillations [53] has not been discussed in this review due to the space limitations for the publication.…”

A widely tunable few-electron droplet

“…Finally, we explore the deformation of the few electron droplet into a serial double quantum dot by means of changing gate voltages. The transport spectrum of this artificial molecule has been described in previous publications for the low electron number limit (0 ≤ N ≤ 2) [11,12,13,16].…”