Abstract
Ground-state 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 intra-layer correlation and ones dominated by inter-layer correlation. The position of the crossover is governed by the strength of the inter-layer electron tunneling and magnetic field. The magic numbers should have an observable effect on the far infra-red optical absorption spectrum, since Kohn's theorem 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 intra-layer and inter-layer correlations, the spin blockade is easier to realize in double dots than in single dots.
Highlights
Coupled quantum dots have recently attracted much interest, since they open up the possibility of manipulating electron configurations in a threedimensional space
Numerical studies of few electron systems confined in single quantum dots have shown that the angular momentum and spin of the ground state in strong magnetic fields belong to a special series values called magic numbers
If we plot the position and intensity of the peaks in the far infrared (FIR) spectra along with the ground state total angular momentum L and spin S (Figs. 10 and 11), we find a one-to-one correspondence between the magnetic fields at which the absorption line jumps and the magnetic fields at which the total angular momentum and/or the total spin of the ground state changes from one magicnumber state to another
Summary
Coupled quantum dots have recently attracted much interest, since they open up the possibility of manipulating electron configurations in a threedimensional space. Ashoori et al and Wagner et al have looked at the addition spectrum (energies required for adding one additional electron) for single dots in magnetic fields, where a total-spin transition caused by the Coulomb interaction is expected [5,6,7] This reminds us of the fractional quantum Hall effect (FQHE) in the bulk 2D electron system, a manifestation of strong electron correlation in high magnetic fields [8,9,10], where the total spin is a sensitive function of the density of electrons in the Landau levels. The wild change in the spin can cause single-electron tunneling to be blocked in some magnetic field regimes due to spin selection rules as we have proposed recently [19] Evidence that this effect is caused by electron correlation is the occurrence of a re-entrant non-blocked region which is hard to explain by Zeeman-energy considerations.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
