Coulomb localization and exchange modulation in two-electron coupled quantum dots

A general study of the singlet-triplet energy separation (exchange energy) in the two-electron system confined in a realistic double-quantum-dot system is performed using a hybrid multiscale approach where the many-body Schrodinger equation is solved exactly within the full quantum dot device environment. The exchange energy is computed as a function of the gate confinement and magnetic field. In particular, it is found that at zero magnetic field the exchange energy varies from meV to sub-mu eV values as the confinement gate biases (tunneling barrier) are changed and the system is driven from a single quantum dot to two coupled quantum dots. The small values of the exchange coupling in this structure are attributed to the large interelectron separation arising when the Coulomb repulsion dominates tunneling.