285 research outputs found
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
Vortices in quantum droplets: Analogies between boson and fermion systems
The main theme of this review is the many-body physics of vortices in quantum
droplets of bosons or fermions, in the limit of small particle numbers. Systems
of interest include cold atoms in traps as well as electrons confined in
quantum dots. When set to rotate, these in principle very different quantum
systems show remarkable analogies. The topics reviewed include the structure of
the finite rotating many-body state, universality of vortex formation and
localization of vortices in both bosonic and fermionic systems, and the
emergence of particle-vortex composites in the quantum Hall regime. An overview
of the computational many-body techniques sets focus on the configuration
interaction and density-functional methods. Studies of quantum droplets with
one or several particle components, where vortices as well as coreless vortices
may occur, are reviewed, and theoretical as well as experimental challenges are
discussed.Comment: Review article, 53 pages, 53 figure
Wigner molecules in polygonal quantum dots: A density functional study
We investigate the properties of many-electron systems in two-dimensional
polygonal (triangle, square, pentagon, hexagon) potential wells by using the
density functional theory. The development of the ground state electronic
structure as a function of the dot size is of particular interest. First we
show that in the case of two electrons, the Wigner molecule formation agrees
with the previous exact diagonalization studies. Then we present in detail how
the spin symmetry breaks in polygonal geometries as the spin density functional
theory is applied. In several cases with more than two electrons, we find a
transition to the crystallized state, yielding coincidence with the number of
density maxima and the electron number. We show that this transition density,
which agrees reasonably well with previous estimations, is rather insensitive
to both the shape of the dot and the electron number.Comment: 8 pages, 11 figure
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
Ground-state of two-dimensional finite electron systems in the Quantum Hall regime
We study electronic structures of quasi-two-dimensional finite electron
systems in high magnetic fields. The solutions in the fractional quantum Hall
regime are interpreted as quantum liquids of electrons and off-electron
vortices. The ground states are classified according to the number of vortices
inside the electron droplet. The theory predicts observable effects due to
vortex formation in the chemical potentials and magnetization of electron
droplets. We compare the transitions in the theory to those found in electron
transport experiments on a quantum dot device and find significant
correspondence.Comment: 4 pages, 4 figures (3 in colour), revised in response to referees'
comments, to appear in Phys. Rev. let
Vortex Clusters in Quantum Dots
We study electronic structures of two-dimensional quantum dots in strong magnetic fields using mean-field density-functional theory and exact diagonalization. Our numerically accurate mean-field solutions show a reconstruction of the uniform-density electron droplet when the magnetic field flux quanta enter one by one the dot in stronger fields. These quanta correspond to repelling vortices forming polygonal clusters inside the dot. We find similar structures in the exact treatment of the problem by constructing a conditional operator for the analysis. We discuss important differences and limitations of the methods used.Peer reviewe
Stability of vortex structures in quantum dots
We study the stability and structure of vortices emerging in two-dimensional quantum dots in high magnetic fields. Our results obtained with exact diagonalization and density-functional calculations show that vortex structures can be found in various confining potentials. In nonsymmetric external potentials we find off-electron vortices that are localized giving rise to charge deficiency or holes in the electron density with rotating currents around them. We discuss the role of quantum fluctuations and show that vortex formation is observable in the energetics of the system. Our findings suggest that vortices can be used to characterize the solutions in high magnetic fields, giving insight into the underlying internal structure of the electronic wave function.Peer reviewe
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