Fractional orbital occupation of spin and charge in artificial atoms

We present results on spin and charge correlations in two-dimensional quantum dots as a function of increasing Coulomb strength (dielectric constant). We look specifically at the orbital occupation of both spin and charge. We find that charge and spin evolve separately, especially at low Coulomb strength. For the charge, we find that a hole develops in the core orbitals at strong Coulomb repulsion, invalidating the common segregation of confined electrons into an inert core and active valence electrons. For excitations, we find a total spin-projection $S_z = -1/2$ breaks apart into separate occupations of positive and negative spin. This dissociation is caused by spin correlations alone. Quantum fluctuations arising from long-range Coulomb repulsion destroy the spin dissociation and eventually results in all orbitals carrying a negative spin.