External field control of a few-particle-bound states in double quantum dots

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We study both spin and charge correlations between two electrons in vertically coupled quantum dots with a finite well width using a diffusion quantum Monte Carlo method, and clarify mechanism of their dependences on both a barrier thickness and a magnetic field on the basis of analysis in the Hubbard model.When the barrier thickness increases, two-electron occupation probability in the same dot is suppressed drastically by enhanced charge correlation relative to electron transfer effect and the magnitude of the anti-ferromagnetic spin coupling decreases in two stages.By applying magnetic field, both the anti-ferromagnetic spin coupling and the two-electron occupation probability in the same dot are suppressed, being caused by enhanced intra-dot charge correlation.In the case of weak lateral confinement in dots, serial switching of the ground states can also be induced by increasing magnetic field and alternation of spin coupling between anti-ferromagnetic coupling and ferromagnetic coupling occurs.