Spin configurations in circular and rectangular vertical quantum dots in a magnetic field: Three-dimensional self-consistent simulations

The magnetic field dependence of the electronic properties of real single vertical quantum dots in circular and rectangular mesas is investigated within a full three-dimensional multiscale self-consistent approach without any á priori assumptions about the shape and strength of the confinement potential. The calculated zero field electron addition energies are in good agreement with available experimental data for both mesa geometries. Charging diagrams in a magnetic field for number of electrons up to five are also computed. Consistent with the experimental data, we found that the charging curves for the rectangular mesa dot in a magnetic field are flatter and exhibit less features than for a circular mesa dot. Evolution of the singlet-triplet energy separation in the two electron system for both dot geometries in magnetic field was also investigated. In the limit of large field, beyond the singlet-triplet transition, the singlet-triplet energy difference continues to become more negative in a circular mesa dot without any saturation within the range of considered magnetic fields while it is predicted to asymptotically approach zero for the rectangular mesa dot. This different behavior is attributed to the symmetry "breaking" that occurs in the singlet wave-functions in the rectangular mesa dot but not in the circular one.