152 research outputs found
Non-linear magneto-transport through small quantum dots at strong intra-dot correlations
Nonlinear transport through a quantum dot is studied in the limit of weak and
strong intra-dot Coulomb interaction. For the latter regime the nonequilibrium
self-consistent mean field equations for energies and spectral weights of
one-electron transitions are formulated. The increase of the bias-voltage
window leads to a strong deviation from Gibbs statistics: the populations of
states involved into a tunnelling are equalizing in this limit even at low
temperature. For a symmetric coupling of a quantum dot to two leads we provide
simple analytical relations between heights of the current steps and degeneracy
of a spectrum in a two-dimensional parabolic dot in a perpendicular magnetic
field in the both regimes.Comment: 40 preprint pages, 6 figure
Klein collimation by rippled graphene superlattice
The hybridization of and orbitals of carbon atoms in graphene
depends on the surface curvature. Considering a single junction between flat
and rippled graphene subsystems, it is found an accumulation of charge in the
rippled subsystem due to Klein penetration phenomenon that gives rise to n-p
junction. Using this fact, we show that the momentum distribution of electrons
in ballisitically propagating beam can be selective without a waveguide, or
external electric, and/or magnetic fields in graphene strip under
experimentally feasible one-dimensional periodic potential. Such a potential is
created with the aid of superlattice that consists of periodically repeated
graphene pieces withdifferent hybridizations of carbon orbits, produced by
variation of the graphene surface curvature. The charge redistribution and
selected transmission of electrons, caused by the superlattice, allows to
control the electron focusing in the considered system by simply changing the
element properties in the superlatticeComment: 17 pages, 7 figure
Analytic solutions to the problem of Coulomb and confining potentials
The oscillator representation method is presented and used to calculate the
energy spectra for a superposition of Coulomb and power-law potentials and for
Coulomb and Yukawa potentials. The method provides an efficient way to obtain
analytic results for arbitrary values of the parameters specifying the
above-type potentials. The calculated energies of the ground and excited states
of the quantum systems in question are found to comply well with exact results.Comment: 25 pages (Latex
Triplet absorption spectroscopy and electromagnetically induced transparency
Coherence phenomena in four-level atomic system, cyclicly driven by three
coherent fields, are investigated thoroughly at zero and weak magnetic fields.
Each strongly interacting atomic state is converted to a triplet due to a
dynamical Stark effect. Two dark lines with a Fano-like profile are arising in
the triplet absorption spectrum with anomalous dispersions. We provide the
conditions to control the widths of the transparency windows by means of the
relative phase of the driving fields and the intensity of the microwave field,
that closes the optical system loop. The effect of the Doppler broadening on
results of the triplet absorption spectroscopy is analysed in detail.Comment: 11 pages, 7 figure
Entanglement as an indicator of a geometrical crossover in a two-electron quantum dot in a magnetic field
We found that a downwardly concave entanglement evolution of the ground state
of a two-electron axially symmetric quantum dot testifies that a shape
transition from a lateral to a vertical localization of two electrons under a
perpendicular magnetic field takes place. Although affected, the two-electron
probability density does not exhibit any prominent change.Comment: 4 pages, 2 figures. arXiv admin note: substantial text overlap with
arXiv:1112.347
Self-Consistent Harmonic Oscillator Model and Tilted Rotation
The three dimensional harmonic oscillator model including a cranking term is
used for an energy variational calculation. Energy minima are found under
variation of the three oscillator frequencies determining the shape of the
system for given values of the three components of the rotational vector which
determines the orientation of the angular momentum in the intrinsic frame.
Tilted rotations are established by numerical means for triaxial nuclei. The
onset of tilted rotations is related to an instability of the mean field as
verified by the random phase approximation. Analytic expressions are derived
for the critical rotational frequencies associated with the mean field
instability.Comment: 16 pages, 2 figures, extended versio
Magnetic alteration of entanglement in two-electron quantum dots
Quantum entanglement is analyzed thoroughly in the case of the ground and
lowest states of two-electron axially symmetric quantum dots under a
perpendicular magnetic field. The individual-particle and the center-of-mass
representations are used to study the entanglement variation at the transition
from interacting to noninteracting particle regimes. The mechanism of symmetry
breaking due to the interaction, that results in the states with symmetries
related to the later representation only, being entangled even at the vanishing
interaction, is discussed. The analytical expression for the entanglement
measure based on the linear entropy is derived in the limit of noninteracting
electrons. It reproduces remarkably well the numerical results for the lowest
states with the magnetic quantum number M>2 in the interacting regime. It is
found that the entanglement of the ground state is a discontinuous function of
the field strength. A method to estimate the entanglement of the ground state,
characterized by the quantum number M, with the aid of the magnetic field
dependence of the addition energy is proposed.Comment: 21 pages, 7 figure
Shape transitions in two-body systems: two-electron quantum dots in a magnetic field
We present a thorough analysis of the electron density distribution (shape)
of two electrons, confined in the three-dimensional harmonic oscillator
potential, as a function of the perpendicular magnetic field.Explicit algebraic
expressions are derived in terms of the system's parameters and the magnetic
field strength to trace the shape transformations in the ground and low-lying
excited states. We found that the interplay of the classical and quantum
properties lead to a quantum shape transition from a lateral to a vertical
localization of electrons in low-lying excited states at relatively strong
Coulomb interaction with alteration of the magnetic field. In contrast, in that
regime in the ground states the electrons form always a ring type distribution
in the lateral plane. The analytical results demonstrate a good agreement with
quantum numerical results near the transition point and at high magnetic field.Comment: 15 pages, 12 figure
Magnetic Field Dependence of Magic Numbers in Small Quantum Dots
It is argued that various kind of shell structure which occurs at specific
values of the magnetic field should be observable in small quantum dots in the
addition energies and the magnetic susceptibility.Comment: 4 pages (Latex file) including 4 epsi figures. For enquires see
e-mail addresses at the end of the pape
Thomson rings in a disk
We discuss the basic principles of a self-organization of a finite number of
charged particles interacting via the 1/r Coulomb potential in a disk geometry.
Our approach is based on the cyclic symmetry and periodicity of the Coulomb
interaction between particles located on several rings. As a result, a system
of equations is derived, which allows us readily to determine with a high
accuracy the equilibrium configurations of a few hundreds charged particles.
For we predict the formation of a hexagonal core and valence
circular rings for the centered configurations.Comment: 13 pages, 3 figures, 1 table. Published version with a new figure and
extended discussio
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