6,305 research outputs found
Metastability and paramagnetism in superconducting mesoscopic disks
A projected order parameter is used to calculate, not only local minima of
the Ginzburg-Landau energy functional, but also saddle points or energy
barriers responsible for the metastabilities observed in superconducting
mesoscopic disks (Geim et al. Nature {\bf 396}, 144 (1998)). We calculate the
local minima magnetization and find the energetic instability points between
vortex configurations with different vorticity. We also find that, for any
vorticity, the supercurrent can reverse its flow direction on decreasing the
magnetic field before one vortex can escape.Comment: Modified version as to appear in Phys. Rev. Let
Vortices in a rotating BEC under extreme elongation
We investigate a non-axisymmetric rotating BEC in a limit of rotation
frequency for which the BEC transforms into a quasi-one-dimensional system. We
compute the vortex lattice wavefunction by minimizing the Gross-Pitaevskii
energy functional in the lowest Landau level approximation for different
confinement potentials. The condensate typically presents a changing number of
vortex rows as a function of the interaction strength or rotation-confinement
ratio. More specifically, the vortex lattices can be classified into two
classes according to their symmetry with respect to the longitudinal axis.
These two classes correspond to different local minima of the energy functional
and evolve independently as a function of the various parameters.Comment: 8 pages, 12 figure
Many-body excitations in tunneling current spectra of a few-electron quantum dot
Inherent asymmetry in the tunneling barriers of few-electron quantum dots
induces intrinsically different tunneling currents for forward and reverse
source-drain biases in the non-linear transport regime. Here we show that in
addition to spin selection rules, overlap matrix elements between many-body
states are crucial for the correct description of tunneling transmission
through quantum dots at large magnetic fields. Signatures of excited
(N-1)-electron states in the transport process through the N-electron system
are clearly identified in the measured transconductances. Our analysis clearly
confirms the validity of single-electron quantum transport theory in quantum
dots.Comment: 5 pages, 2 figure
Simulation Application for the LHCb Experiment
We describe the LHCb detector simulation application (Gauss) based on the
Geant4 toolkit. The application is built using the Gaudi software framework,
which is used for all event-processing applications in the LHCb experiment. The
existence of an underlying framework allows several common basic services such
as persistency, interactivity, as well as detector geometry description or
particle data to be shared between simulation, reconstruction and analysis
applications. The main benefits of such common services are coherence between
different event-processing stages as well as reduced development effort. The
interfacing to Geant4 toolkit is realized through a facade (GiGa) which
minimizes the coupling to the simulation engine and provides a set of abstract
interfaces for configuration and event-by-event communication. The Gauss
application is composed of three main blocks, i.e. event generation, detector
response simulation and digitization which reflect the different stages
performed during the simulation job. We describe the overall design as well as
the details of Gauss application with a special emphasis on the configuration
and control of the underlying simulation engine. We also briefly mention the
validation strategy and the planing for the LHCb experiment simulation.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 6 pages, LaTeX, 9 eps figures. PSN
TUMT00
An effective lowest Landau level treatment of demagnetization in superconducting mesoscopic disks
Demagnetization, which is inherently present in the magnetic response of
small finite-size superconductors, can be accounted for by an effective
within a two-dimensional lowest Landau level approximation of the
Ginzburg-Landau functional. We show this by comparing the equilibrium
magnetization of superconducting mesoscopic disks obtained from the numerical
solution of the three-dimensional Ginzburg-Landau equations with that obtained
in the ``effective'' LLL approximation.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Capacitance spectroscopy in quantum dots: Addition spectra and decrease of tunneling rates
A theoretical study of single electron capacitance spectroscopy in quantum
dots is presented. Exact diagonalizations and the unrestricted Hartree-Fock
approximation have been used to shed light over some of the unresolved aspects.
The addition spectra of up to 15 electrons is obtained and compared with the
experiment. We show evidence for understanding the decrease of the single
electron tunneling rates in terms of the behavior of the spectral weight
function. (To appear in Phys. Rev. B (Rapid Comm.))Comment: 10 pages, Revtex, hard copy or PostScript Figures upon request on
[email protected]
Correlated few-electron states in vertical double-quantum-dot systems
The electronic properties of semiconductor, vertical, double quantum dot
systems with few electrons are investigated by means of analytic,
configuration-interaction, and mean-field methods. The combined effect of a
high magnetic field, electrostatic confinement, and inter-dot coupling, induces
a new class of few-electron ground states absent in single quantum dots. In
particular, the role played by the isospin (or quantum dot index) in
determining the appearance of new ground states is analyzed and compared with
the role played by the standard spin.Comment: 20 pages, Latex, figures upon request. To appear in Phys. Rev. B
(January 1995
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