17 research outputs found
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
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
Optimal confinement potential in quantum Hall droplets
We find that the confinement potential of a few electron quantum dot can be
tuned to significantly increase the overlap with certain quantum Hall trial
wave functions. Besides manipulating inter-electron interaction, this approach
may prove useful in quantum point contact experiments, which involve narrow
constrictions.Comment: 4 pages, 1 figur
Graphene: from materials science to particle physics
Since its discovery in 2004, graphene, a two-dimensional hexagonal carbon
allotrope, has generated great interest and spurred research activity from
materials science to particle physics and vice versa. In particular, graphene
has been found to exhibit outstanding electronic and mechanical properties, as
well as an unusual low-energy spectrum of Dirac quasiparticles giving rise to a
fractional quantum Hall effect when freely suspended and immersed in a magnetic
field. One of the most intriguing puzzles of graphene involves the
low-temperature conductivity at zero density, a central issue in the design of
graphene-based nanoelectronic components. While suspended graphene experiments
have shown a trend reminiscent of semiconductors, with rising resistivity at
low temperatures, most theories predict a constant or even decreasing
resistivity. However, lattice field theory calculations have revealed that
suspended graphene is at or near the critical coupling for excitonic gap
formation due to strong Coulomb interactions, which suggests a simple and
straightforward explanation for the experimental data. In this contribution we
review the current status of the field with emphasis on the issue of gap
formation, and outline recent progress and future points of contact between
condensed matter physics and Lattice QCD.Comment: 14 pages, 6 figures. Plenary talk given at the XXVIII International
Symposium on Lattice Field Theory (Lattice 2010), June 14-19, 2010,
Villasimius, Sardinia, Ital
Quantum Hall droplet laterally coupled to a quantum ring
We study a two-dimensional cylindrically-symmetric electron droplet separated
from a surrounding electron ring by a tunable barrier using the exact
diagonalization method. The magnetic field is assumed strong so that the
electrons become spin-polarized and reside on the lowest Fock-Darwin band. We
calculate the ground state phase diagram for 6 electrons. At weak coupling, the
phase diagram exhibits a clear diamond structure due to the blockade caused by
the angular momentum difference between the two systems. We find separate
excitations of the droplet and the ring as well as the transfer of charge
between the two parts of the system. At strong coupling, interactions destroy
the coherent structure of the phase diagram, while individual phases are still
heavily affected by the potential barrier.Comment: 7 pages, 7 figure
Fractional periodicity and magnetism of extended quantum rings
The magnetic properties and nature of the persistent current in small
flux-penetrated rings are investigated. An effective rigid-rotator
description is formulated for this system, which coincides with a transition to
a ferromagnetic state in the model. The criteria for the onset of effective
rigid rotation is given. The model is used to understand continuum model
ground-state solutions for a 2D few-particle hard-wall quantum dot, where
ferromagnetic solutions are found even without the Zeeman coupling to spin.
After the onset of effective rigid rotation, a 97--98% correspondence can be
determined between the lattice model and continuum model eigenstate results
Graphene: From materials science to particle physics
Since its discovery in 2004, graphene, a two-dimensional hexagonal carbon allotrope, has generated great interest and spurred research activity from materials science to particle physics and vice versa. In particular, graphene has been found to exhibit outstanding electronic and mechanical properties, as well as an unusual low-energy spectrum of Dirac quasiparticles giving rise to a fractional quantum Hall effect when freely suspended and immersed in a magnetic field. One of the most intriguing puzzles of graphene involves the low-temperature conductivity at zero density, a central issue in the design of graphene-based nanoelectronic components. While suspended graphene experiments have shown a trend reminiscent of semiconductors, with rising resistivity at low temperatures, most theories predict a constant or even decreasing resistivity. However, lattice field theory calculations have revealed that suspended graphene is at or near the critical coupling for excitonic gap formation due to strong Coulomb interactions, which suggests a simple and straightforward explanation for the experimental data. In this contribution we review the current status of the field with emphasis on the issue of gap formation, and outline recent progress and future points of contact between condensed matter physics and Lattice QCD
Magnetism in tunable quantum rings
We have studied the spin structure of circular four-electron quantum rings
using tunable confinement potentials. The calculations were done using the
exact diagonalization method. Our results indicate that ringlike systems can
have oscillatory flips between ferromagnetic and antiferromagnetic behaviour as
a function of the magnetic field. Furthermore, at constant external magnetic
fields there were seen similar oscillatory changes between ferromagnetism and
antiferromagnetism when the system parameters were changed. Ackording to our
results, the magnetism of quantum rings could be tuned by system parameters.We
have studied the spin structure of circular four-electron quantum rings using
tunable confinement potentials. The calculations were done using the exact
diagonalization method. Our results indicate that ringlike systems can have
oscillatory flips between ferromagnetic and antiferromagnetic behaviour as a
function of the magnetic field. Furthermore, at constant external magnetic
fields there were seen similar oscillatory changes between ferromagnetism and
antiferromagnetism when the system parameters were changed. According to our
results, the magnetism of quantum rings could be tuned by system parameters.Comment: 5 pages, 3 figures, article. Typo correcte