Vertically coupled double quantum dots in magnetic fields

Ground- and excited-state properties of vertically coupled double quantum dots are studied by exact diagonalization. Magic-number total angular momenta that minimize the total energy are found to reflect a crossover between electron configurations dominated by intralayer correlation and those dominated by interlayer correlation. The position of the crossover is governed by the strength of the interlayer electron tunneling and magnetic field. The magic numbers should have an observable effect on the far-infrared optical-absorption spectrum, since Kohn’s theorem [Phys. Rev. 123, 1242 (1961)] does not hold when the confinement potential is different for two dots. This is indeed confirmed here from a numerical calculation that includes Landau-level mixing. Our results take full account of the effect of spin degrees of freedom. A key feature is that the total spin S of the system and the magic-number angular momentum are intimately linked because of strong electron correlation. Thus S jumps hand in hand with the total angular momentum as the magnetic field is varied. One important consequence of this is that the spin blockade (an inhibition of single-electron tunneling) should occur in some magnetic field regions because of a spin selection rule. Owing to the flexibility arising from the presence of both intralayer and interlayer correlations, the spin blockade is easier to realize in double dots than in single dots.