Addition energy spectrum of a quantum dot disk up to the third shell

The 0 T addition energy spectrum for a high quality circular semiconductor quantum dot artificial atom is measured directly from the Coulomb diamonds up to 12 electrons. We focus on the way electrons fill the third shell. Attention is paid in particular to the entry of the first and second electrons to the third shell levels as deduced from the weak magnetic field dependence. The experimental third shell spectrum is then compared to spectra generated from a 3-dimensional density functional calculation, and a modified parabolic potential and constant interaction model.