  We study a two-dimensional cylindrically-symmetric electron droplet separated
from a surrounding electron ring by a tunable barrier using the exact
diagonalization method. The magnetic field is assumed strong so that the
electrons become spin-polarized and reside on the lowest Fock-Darwin band. We
calculate the ground state phase diagram for 6 electrons. At weak coupling, the
phase diagram exhibits a clear diamond structure due to the blockade caused by
the angular momentum difference between the two systems. We find separate
excitations of the droplet and the ring as well as the transfer of charge
between the two parts of the system. At strong coupling, interactions destroy
the coherent structure of the phase diagram, while individual phases are still
heavily affected by the potential barrier.
