2 research outputs found
Magic Numbers and Optical Absorption Spectrum in Vertically Coupled Quantum Dots in the Fractional Quantum Hall Regime
Exact diagonalization is used to study the quantum states of vertically
coupled quantum dots in strong magnetic fields. We find a new sequence of
angular momentum magic numbers which are a consequence of the electron
correlation in the double dot. The new sequence occurs at low angular momenta
and changes into the single dot sequence at a critical angular momentum
determined by the strength of the inter-dot electron tunneling. We also propose
that the magic numbers can be investigated experimentally in vertically coupled
dots. Because of the generalized Kohn theorem, the far-infrared optical
absorption spectrum of a single dot is unaffected by correlation but the
theorem does not hold for two vertically coupled dots which have different
confining potentials. We show that the absorption energy of the double dot
should exhibit discontinuities at the magnetic fields where the total angular
momentum changes from one magic number to another.Comment: 4 pages, 3 Postscript figures, RevTeX. (to appear in Phys.Rev.B
Vertically coupled double quantum dots in magnetic fields
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, , of the system and the magic-number angular momentum are
intimately linked because of strong electron correlation. Thus 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.Comment: to be published in Phys. Rev. B1