Three electrons in laterally coupled quantum dots: Tunnel vs electrostatic coupling, ground-state symmetry, and interdot correlations

The phase diagram for the ground-state symmetry of three electrons confined in a pair of laterally coupled dots is determined as function of the interdot distance and the magnetic field. With a few exceptions the ground-state spin and parity symmetry sequence of a circular harmonic quantum dot is conserved. Reentrant behavior of some energy levels as ground states is found as a function of the magnetic field. The disappearance of interdot tunnelling due to a strong magnetic field leads to ground-state degeneracy of the even and odd parity energy levels. It is shown that at a high magnetic field the system can be closely approximated by a two-electron system confined in one dot and a spectator electron localized in the other. Broken-parity eigenstates with a classical charge distribution are constructed and used to discuss the interdot electron-electron correlations.