RKKY Interaction in Coupled Quantum Dots

Abstract

In artificial nanostructures the control of localized, single spin is of great technological importance for nanospintronic applications. In that respect quantum dots (QD), as the building blocks of nanodevices, seem to be most perspective. Quantum dots are electronic systems which confine a well-defined number of electrons. The total spin of a dot can be integer or half-integer (the latter stands for odd number of confined electrons). Typical nanodevices are composed of a few QD interconnected by leads. Electrons (from a lead or metallic substrate) scattered off QD spins induce an effective spin exchange interaction, the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction [1]. Magnetic correlations of QDs spins arising from the RKKY interaction are very important as they affect conductivity, an effect of primary importance for spintronics. Magnetic moments of QDs are Kondo (partially) screened, so the strength of the RKKY coupling depends both on the QDs separation and the Kondo screening. The Kondo screening can be tuned by the gate voltage; this effect offers an opportunity to control the strength of the effective RKKY exchange. Such a tuned RKKY interaction between QD moments is deemed as a possible way to couple QD based qubits in construction of universal quantum logic gates. We focus our attention on the study of pure RKKY coupling between two dots joined by a lead, leaving the Kondo contribution aside. Two distinct configurations of interacting QDs are considered; the interaction via electrons of a substrate and the other one via electrons of metallic lead which joins adjacent dots. The problem of formation of long-range magnetic order within a quasi-1D ferromagnetic lead is discussed independently.