  We investigate theoretically the transport properties of two independent
artificial Kondo impurities. They are coupled together via a tunable
Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction. For strong enough
antiferromagnetic RKKY interaction, the impurity density of states increases
with the applied in-plane magnetic field. This effect can be used to
distinguish between antiferromagnetic and ferromagnetic RKKY interactions.
These results may be relevant to explain some features of recent experiments by
Craig et al. (cond-mat/0404213).
