Two-impurity Anderson model revisited: Competition between Kondo effect and reservoir-mediated superexchange in double quantum dots

We study a series-coupled double quantum dot in the Kondo regime modeled by the two-impurity Anderson model and find a conduction-band-mediated superexchange interaction that competes with Kondo physics in the strong Coulomb interaction limit. Our numerical renormalization-group results complemented with the higher-order Rayleigh-Schroumldinger perturbation theory show that the exchange mechanism leads to clear experimental consequences that can be checked in transport measurements through double quantum dots.