Electronic asymmetry in self-assembled quantum dot molecules made of identical InAs/GaAs quantum dots

We show that a diatomic dot molecule made of two identical, vertically stacked, strained InAs/GaAs self-assembled dots exhibits an asymmetry in its single- and many-particle wave functions. The single particle wave function is asymmetric due to the inhomogeneous strain, while the asymmetry of the many-particle wave functions is caused by the correlation-induced localization: the lowest singlet (1)Sigma(g) and triplet (3)Sigma states show that the two electrons are each localized on different dots within the molecule; for the next singlet states (1)Sigma(u) both electrons are localized on the same (bottom) dot for interdot separation d > 8 nm. The singlet-triplet splitting is found to be similar to 0.1 meV at interdot separation d=9 nm and as large as 100 meV for d=4 nm, orders of magnitude larger than the few meV found in the large (50-100 nm) electrostatically confined dots.