976 research outputs found
Variational Monte Carlo for Interacting Electrons in Quantum Dots
We use a variational Monte Carlo algorithm to solve the electronic structure
of two-dimensional semiconductor quantum dots in external magnetic field. We
present accurate many-body wave functions for the system in various magnetic
field regimes. We show the importance of symmetry, and demonstrate how it can
be used to simplify the variational wave functions. We present in detail the
algorithm for efficient wave function optimization. We also present a Monte
Carlo -based diagonalization technique to solve the quantum dot problem in the
strong magnetic field limit where the system is of a multiconfiguration nature.Comment: 34 pages, proceedings of the 1st International Meeting on Advances in
Computational Many-Body Physics, to appear in Journal of Low Temperature
Physics (vol. 140, nos. 3/4
Reduced density-matrix functional theory in quantum Hall systems
We apply reduced density-matrix functional theory to the parabolically
confined quantum Hall droplet in the spin-frozen strong magnetic field regime.
One-body reduced density matrix functional method performs remarkably well in
obtaining ground states, energies, and observables derivable from the one-body
reduced density matrix for a wide range of system sizes. At the strongly
correlated regime, the results go well beyond what can be obtained with the
density functional theory. However, some of the detailed properties of the
system, such as the edge Green's function, are not produced correctly unless we
use the much heavier two-body reduced density matrix method.Comment: 13 pages, 7 figure
Fractional periodicity of persistent current in coupled quantum rings
We study the transmission properties of a few-site Hubbard rings with up to
second-nearest neighbor coupling embedded to a ring-shaped lead using exact
diagonalization. The approach captures all the correlation effects and enables
us to include interactions both in the ring and in the ring-shaped lead, and
study on an equal footing weak and strong coupling between the ring and the
lead as well as asymmetry. In the weakly coupled case, we find fractional
periodicity at all electron fillings at sufficiently high Hubbard U, similar to
isolated rings. For strongly coupled rings, on the contrary, fractional
periodicity is only observed at sufficiently large negative gate voltages and
high interaction strengths. This is explained by the formation of a bound
correlated state in the ring that is effectively weakly coupled to the lead
Effects of thickness in quantum dots at strong magnetic fields
We study the effects of thickness on the ground states of two-dimensional
quantum dots in high magnetic fields. To be specific, we assume the thickness
to be small so that only the lowest state in the corresponding direction is
occupied, but which however leads to a modification of the effective
interaction between the electrons. We find the ground state phase diagram and
demonstrate the emergence of new phases as the thickness is accounted for.
Finally, the wave functional form and vortex structure of different phases is
analyzed.Comment: 5 pages, 4 figure
Singlet-triplet oscillations and far-infrared spectrum of four-minima quantum-dot molecule
We study ground states and far-infrared spectra (FIR) of two electrons in
four-minima quantum-dot molecule in magnetic field by exact diagonalization.
Ground states consist of altering singlet and triplet states, whose frequency,
as a function of magnetic field, increases with increasing dot-dot separation.
When the Zeeman energy is included, only the two first singlet states remain as
ground states. In the FIR spectra, we observe discontinuities due to crossing
ground states. Non-circular symmetry induces anticrossings, and also an
additional mode above in the spin-triplet spectrum. In particular,
we conclude that electron-electron interactions cause only minor changes to the
FIR spectra and deviations from the Kohn modes result from the low-symmetry
confinement potential.Comment: 4 pages, 3 figures, QD2004 conference paper, accepted in Physica
Half-Integer Filling Factor States in Quantum Dots
Emergence of half-integer filling factor states, such as nu=5/2 and 7/2, is
found in quantum dots by using numerical many-electron methods. These states
have interesting similarities and differences with their counterstates found in
the two-dimensional electron gas. The nu=1/2 states in quantum dots are shown
to have high overlaps with the composite fermion states. The lower overlap of
the Pfaffian state indicates that electrons might not be paired in quantum dot
geometry. The predicted nu=5/2 state has high spin polarization which may have
impact on the spin transport through quantum dot devices.Comment: 4 pages, accepted to Phys. Rev. Let
Charge dynamics in two-electron quantum dots
We investigate charge dynamics in a two-electron double quantum dot. The
quantum dot is manipulated by using a time-dependent external voltage that
induces charge oscillations between the dots. We study the dependence of the
charge dynamics on the external magnetic field and on the periodicity of the
external potential. We find that for suitable parameter values, it is possible
to induce both one-electron and two-electron oscillations between the dots.Comment: 4 pages, 7 figures, proceedings of the Quantum Dot 2010 conferenc
Role of interactions in the far-infrared spectrum of a lateral quantum dot molecule
We study the effects of electron-electron correlations and confinement
potential on the far-infrared spectrum of a lateral two-electron quantum dot
molecule by exact diagonalization. The calculated spectra directly reflect the
lowered symmetry of the external confinement potential. Surprisingly, we find
interactions to drive the spectrum towards that of a high-symmetry parabolic
quantum dot. We conclude that far-infrared spectroscopy is suitable for probing
effective confinement of the electrons in a quantum dot system, even if
interaction effects cannot be resolved in a direct fashion.Comment: 4 pages, 2 figure
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