  We study the "phase diagram" of a Hubbard plaquette with Rashba spin-orbit
coupling. We show that the peculiar way in which Rashba coupling breaks the
spin-rotational symmetry of the Hubbard model allows a mixing of singlet and
triplet components in the ground-state that slows down and it changes the
nature of the Mott transition and of the Mott insulating phases.
