  We study coupled semiconductor quantum dots theoretically through a
generalized Hubbard approach, where intra- and inter-dot Coulomb Correlation,
as well as tunneling effects are described on the basis of realistic electron
wavefunctions. We find that the ground-state configuration of
vertically-coupled double dots undergoes non-trivial quantum transitions as a
function of the inter-dot distance d; at intermediate values of d we predict a
new phase that should be observable in the addition spectra and in the
magnetization changes.
