Kondo screening cloud in a double quantum dot system

We analyze the transport properties of two artificial magnetic impurities coupled together via a tunable Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction mediated by conduction electrons of a finite-size one-dimensional wire. We show that the sign of the RKKY interaction can be controlled by gating the wire. We investigate the interplay between finite-size effects and RKKY interaction and found that the two artificial impurities start to interact to each other as soon as the Kondo screening cloud length becomes larger than the length of the wire. This should allow one to give a lower experimental estimate of the Kondo screening cloud length.

Figure 1

Schematic representation of the device under study. The two quantum dots are connected to a finite-size open wire. The Fermi level in the wire is controlled by a gate voltage $E_W$.

Figure 2

Example of the local density of states seen by the dot 1. We took $2l=22$ and ${\gamma }_W^2=0.25$.

Figure 3

RKKY interaction as a function of $E_W$. We took the same parameter as in Fig. 2: $2l=22$ and ${\gamma }_W^2=0.25$. When $E_W$ is tuned on a resonance, the RKKY interaction becomes positive and gets enhanced by a factor $\sim 1∕{\gamma }_W^2$ as predicted by Eq. (24).