SHELL FILLING AND SPIN EFFECTS IN A FEW ELECTRON QUANTUM-DOT

We study atomiclike properties of artificial atoms by measuring Coulom b oscillations in vertical quantum dots containing a tunable number of electrons starting from zero. At zero magnetic field the energy neede d to add electrons to a dot reveals a shell structure for a two-dimens ional harmonic. potential. As a function of magnetic field the current peaks shift in pairs, due to the filling of electrons into spin-degen erate single-particle states. When the magnetic field is sufficiently small, however,the pairing is modified, as predicted by Hund's rule, t o favor the filling of parallel spins.