283 research outputs found
Confinement of two-dimensional excitons in a non-homogeneous magnetic field
The effective Hamiltonian describing the motion of an exciton in an external
non-homogeneous magnetic field is derived. The magnetic field plays the role of
an effective potential for the exciton motion, results into an increment of the
exciton mass and modifies the exciton kinetic energy operator. In contrast to
the homogeneous field case, the exciton in a non-homogeneous magnetic field can
also be trapped in the low field region and the field gradient increases the
exciton confinement. The trapping energy and wave function of the exciton in a
GaAs two-dimensional electron gas for specific circular magnetic field
configurations are calculated. The results show than excitons can be trapped by
non-homogeneous magnetic fields, and that the trapping energy is strongly
correlated with the shape and strength of the non-homogeneous magnetic field
profile.Comment: 9 pages, 12 figure
N electrons in a quantum dot: Two-point Pade approximants
We present analytic estimates for the energy levels of N electrons (N = 2 -
5) in a two-dimensional parabolic quantum dot. A magnetic field is applied
perpendicularly to the confinement plane. The relevant scaled energy is shown
to be a smooth function of the parameter \beta=(effective Rydberg/effective dot
energy)^{1/6}. Two-point Pade approximants are obtained from the series
expansions of the energy near the oscillator () and Wigner
() limits. The approximants are expected to work with an error
not greater than 2.5% in the entire interval .Comment: 27 pages. LaTeX. 6 figures not include
Currents in a many-particle parabolic quantum dot under a strong magnetic field
Currents in a few-electron parabolic quantum dot placed into a perpendicular
magnetic field are considered. We show that traditional ways of investigating
the Wigner crystallization by studying the charge density correlation function
can be supplemented by the examination of the density-current correlator.
However, care must be exercised when constructing the correct projection of the
multi-dimensional wave function space. The interplay between the magnetic field
and Euler-liquid-like behavior of the electron liquid gives rise to persistent
and local currents in quantum dots. We demonstrate these phenomena by collating
a quasi-classical theory valid in high magnetic fields and an exact numerical
solution of the many-body problem.Comment: Uses RevTeX4, figures included in the tex
Magnetic edge states of impenetrable stripe
The electron motion in a strong perpendicular magnetic field close to the
impenetrable stripe is considered by making use of the singular integral
equation technique. The energy spectrum is calculated and compared with the
energy spectrum of the round antidot.Comment: REVTeX4 format, 9 pages with 9 figures (*.eps
Dephasing time of disordered two-dimensional electron gas in modulated magnetic fields
The dephasing time of disordered two-dimensional electron gas in a modulated
magnetic field is studied. It is shown that in the weak inhomogeneity limit,
the dephasing rate is proportional to the field amplitude, while in strong
inhomogeneity limit the dependence is quadratic. It is demonstrated that the
origin of the dependence of dephasing time on field amplitude lies in the
nature of corresponding single-particle motion. A semiclassical Monte Carlo
algorithm is developed to study the dephasing time, which is of qualitative
nature but efficient in uncovering the dependence of dephasing time on field
amplitude for arbitrarily complicated magnetic-field modulation. Computer
simulations support analytical results. The crossover from linear to quadratic
dependence is then generalized to the situation with magnetic field modulated
periodically in one direction with zero mean, and it is argued that this
crossover can be expected for a large class of modulated magnetic fields.Comment: 8 pages, 2 figure
Resistance effects due to magnetic guiding orbits
The Hall and magnetoresistance of a two dimensional electron gas subjected to
a magnetic field barrier parallel to the current direction is studied as
function of the applied perpendicular magnetic field. The recent experimental
results of Nogaret {\em et al.} [Phys. Rev. Lett. {\bf 84}, 2231 (2000)] for
the magneto- and Hall resistance are explained using a semi-classical theory
based on the Landauer-B\"{u}ttiker formula. The observed positive
magnetoresistance peak is explained as due to a competition between a decrease
of the number of conducting channels as a result of the growing magnetic field,
from the fringe field of the ferromagnetic stripe as it becomes magnetized, and
the disappearance of snake orbits and the subsequent appearance of cycloidlike
orbits.Comment: 7 pages, 7 figure
The two electron artificial molecule
Exact results for the classical and quantum system of two vertically coupled
two-dimensional single electron quantum dots are obtained as a function of the
interatomic distance (d) and with perpendicular magnetic field. The classical
system exhibits a second order structural transition as a function of d which
is smeared out and shifted to lower d values in the quantum case. The
spin-singlet - spin-triplet oscillations are shifted to larger magnetic fields
with increasing d and are quenched for a sufficiently large interatomic
distance.Comment: 4 pages, 4 ps figure
Pade approximants for the ground-state energy of closed-shell quantum dots
Analytic approximations to the ground-state energy of closed-shell quantum
dots (number of electrons from 2 to 210) are presented in the form of two-point
Pade approximants. These Pade approximants are constructed from the small- and
large-density limits of the energy. We estimated that the maximum error,
reached for intermediate densities, is less than 3%. Within the present
approximation the ground-state is found to be unpolarized.Comment: 4 pages, RevTeX, 3 ps figure
Magnetic Quantum Dot: A Magnetic Transmission Barrier and Resonator
We study the ballistic edge-channel transport in quantum wires with a
magnetic quantum dot, which is formed by two different magnetic fields B^* and
B_0 inside and outside the dot, respectively. We find that the electron states
located near the dot and the scattering of edge channels by the dot strongly
depend on whether B^* is parallel or antiparallel to B_0. For parallel fields,
two-terminal conductance as a function of channel energy is quantized except
for resonances, while, for antiparallel fields, it is not quantized and all
channels can be completely reflected in some energy ranges. All these features
are attributed to the characteristic magnetic confinements caused by nonuniform
fields.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
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