144 research outputs found
Spectra of Harmonium in a magnetic field using an initial value representation of the semiclassical propagator
For two Coulombically interacting electrons in a quantum dot with harmonic
confinement and a constant magnetic field, we show that time-dependent
semiclassical calculations using the Herman-Kluk initial value representation
of the propagator lead to eigenvalues of the same accuracy as WKB calculations
with Langer correction. The latter are restricted to integrable systems,
however, whereas the time-dependent initial value approach allows for
applications to high-dimensional, possibly chaotic dynamics and is extendable
to arbitrary shapes of the potential.Comment: 11 pages, 1 figur
On the lower bound on the exchange-correlation energy in two dimensions
We study the properties of the lower bound on the exchange-correlation energy
in two dimensions. First we review the derivation of the bound and show how it
can be written in a simple density-functional form. This form allows an
explicit determination of the prefactor of the bound and testing its tightness.
Next we focus on finite two-dimensional systems and examine how their distance
from the bound depends on the system geometry. The results for the high-density
limit suggest that a finite system that comes as close as possible to the
ultimate bound on the exchange-correlation energy has circular geometry and a
weak confining potential with a negative curvature
Unpaired and spin-singlet paired states of a two-dimensional electron gas in a perpendicular magnetic field
We present a variational study of both unpaired and spin-singlet paired
states induced in a two-dimensional electron gas at low density by a
perpendicular magnetic field. It is based on an improved circular-cell
approximation which leads to a number of closed analytical results. The
ground-state energy of the Wigner crystal containing a single electron per cell
in the lowest Landau level is obtained as a function of the filling factor
: the results are in good agreement with those of earlier approaches and
predict for the upper filling factor at which the
solid-liquid transition occurs. A novel localized state of spin-singlet
electron pairs is examined and found to be a competitor of the unpaired state
for filling factor . The corresponding phase boundary is quantitatively
displayed in the magnetic field-electron density plane.Comment: 19 pages, 8 figures, submitted to Phys. Rev. B on 7th April 2001. to
appear in Phys. Rev.
Quantum-dot lithium in zero magnetic field: Electronic properties, thermodynamics, and a liquid-solid transition in the ground state
Energy spectra, electron densities, pair correlation functions and heat
capacity of a quantum-dot lithium in zero external magnetic field (a system of
three interacting two-dimensional electrons in a parabolic confinement
potential) are studied using the exact diagonalization approach. A particular
attention is given to a Fermi-liquid -- Wigner-solid transition in the ground
state of the dot, induced by the intra-dot Coulomb interaction.Comment: 12 pages, incl. 16 figure
The evaluation of liver fibrosis regression in chronic hepatitis C patients after the treatment with direct-acting antiviral agents – A review of the literature
The second-generation of direct-acting antiviral agents are the current treatment for chronic viral hepatitis C infection. To evaluate the regression of liver fibrosis in patients receiving this therapy, liver biopsy remains the most accurate method, but the invasiveness of this procedure is its major drawback. Different non-invasive tests have been used to study changes in the stage of liver fibrosis in patients with chronic viral hepatitis treated with the second-generation of direct-acting antiviral agents: liver stiffness measurements (with transient elastography or acoustic radiation force impulse elastography) or different scores that use serum markers to calculate a fibrosis score. We prepared a literature review of the available data regarding the long-term evolution of liver fibrosis after the treatment with direct-acting antiviral agents for chronic viral hepatitis C
Probing the Shape of Quantum Dots with Magnetic Fields
A tool for the identification of the shape of quantum dots is developed. By
preparing a two-electron quantum dot, the response of the low-lying excited
states to a homogeneous magnetic field, i.e. their spin and parity
oscillations, is studied for a large variety of dot shapes. For any geometric
configuration of the confinement we encounter characteristic spin singlet -
triplet crossovers. The magnetization is shown to be a complementary tool for
probing the shape of the dot.Comment: 11 pages, 4 figure
Two Electrons in a Quantum Dot: A Unified Approach
Low-lying energy levels of two interacting electrons confined in a
two-dimensional parabolic quantum dot in the presence of an external magnetic
field have been revised within the frame of a novel model. The present
formalism, which gives closed algebraic solutions for the specific values of
magnetic field and spatial confinement length, enables us to see explicitly
individual effects of the electron correlation.Comment: 14 page
Formation and control of electron molecules in artificial atoms: Impurity and magnetic-field effects
Interelectron interactions and correlations in quantum dots can lead to
spontaneous symmetry breaking of the self-consistent mean field resulting in
formation of Wigner molecules. With the use of spin-and-space unrestricted
Hartree-Fock (sS-UHF) calculations, such symmetry breaking is discussed for
field-free conditions, as well as under the influence of an external magnetic
field. Using as paradigms impurity-doped (as well as the limiting case of
clean) two-electron quantum dots (which are analogs to helium-like atoms), it
is shown that the interplay between the interelectron repulsion and the
electronic zero-point kinetic energy leads, for a broad range of impurity
parameters, to formation of a singlet ground-state electron molecule,
reminiscent of the molecular picture of doubly-excited helium. Comparative
analysis of the conditional probability distributions for the sS-UHF and the
exact solutions for the ground state of two interacting electrons in a clean
parabolic quantum dot reveals that both of them describe formation of an
electron molecule with similar characteristics. The self-consistent field
associated with the triplet excited state of the two-electron quantum dot
(clean as well as impurity-doped) exhibits symmetry breaking of the Jahn-Teller
type, similar to that underlying formation of nonspherical open-shell nuclei
and metal clusters. Furthermore, impurity and/or magnetic-field effects can be
used to achieve controlled manipulation of the formation and pinning of the
discrete orientations of the Wigner molecules. Impurity effects are futher
illustrated for the case of a quantum dot with more than two electrons.Comment: Latex/Revtex, 10 pages with 4 gif figures. Small changes to explain
the difference between Wigner and Jahn-Teller electron molecules. A complete
version of the paper with high quality figures inside the text is available
at http://shale.physics.gatech.edu/~costas/qdhelium.html For related papers,
see http://www.prism.gatech.edu/~ph274c
Collective and independent-particle motion in two-electron artificial atoms
Investigations of the exactly solvable excitation spectra of two-electron
quantum dots with a parabolic confinement, for different values of the
parameter R_W expressing the relative magnitudes of the interelectron repulsion
and the zero-point kinetic energy of the confined electrons, reveal for large
R_W a remarkably well-developed ro-vibrational spectrum associated with
formation of a linear trimeric rigid molecule composed of the two electrons and
the infinitely heavy confining dot. This spectrum transforms to one
characteristic of a "floppy" molecule for smaller values of R_W. The
conditional probability distribution calculated for the exact two-electron wave
functions allows for the identification of the ro-vibrational excitations as
rotations and stretching/bending vibrations, and provides direct evidence
pertaining to the formation of such molecules.Comment: Published version. Latex/Revtex, 5 pages with 2 postscript figures
embedded in the text. For related papers, see
http://www.prism.gatech.edu/~ph274c
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