The Kondo box in the presence of exchange interaction

We study the problem of a quantum dot with finite level spacing which is coupled antiferromagnetically to a Kondo spin (``Kondo box''). In particular, we investigate the influence of a ferromagnetic exchange interaction among the dot electrons and the effect of an applied Zeeman field. This problem is addressed with the help of a numerical algorithm that allows for an exact diagonalization of the Hamiltonian in a good total spin basis [1] of the dot plus the Kondo spin. We discuss how the competition between the ferromagnetic exchange and the antiferromagnetic Kondo interaction affects the ground-state spin of the system. \newline [1] H. Tureci and Y. Alhassid, Phys. Rev. B 74, 165333 (2006).