1,458 research outputs found

### Non-adiabatic Current Excitation in Quantum Rings

We investigate the difference in the response of a one-dimensional
semiconductor quantum ring and a finite-width ring to a strong and short-lived
time-dependent perturbation in the THz regime. In both cases the persistent
current is modified through a nonadiabatic change of the many-electron states
of the system, but by different mechanisms in each case.Comment: LaTeX, 5 pages with 6 embedded postscript figures, submitted to 20th
Nordic Semiconductor Meeting, Tampere (2003

### Turnstile pumping through an open quantum wire

We use a non-Markovian generalized master equation (GME) to describe the
time-dependent charge transfer through a parabolically confined quantum wire of
a finite length coupled to semi-infinite quasi two-dimensional leads. The
quantum wire and the leads are in a perpendicular external magnetic field. The
contacts to the left and right leads depend on time and are kept out of phase
to model a quantum turnstile of finite size. The effects of the driving period
of the turnstile, the external magnetic field, the character of the contacts,
and the chemical potential bias on the effectiveness of the charge transfer of
the turnstile are examined, both in the absence and in the presence of the
magnetic field. The interplay between the strength of the coupling and the
strength of the magnetic field is also discussed. We observe how the edge
states created in the presence of the magnetic field contribute to the pumped
charge.Comment: RevTeX (pdf-LaTeX), 9 pages with 12 included jpg figure

### The evolution of Bernstein modes in quantum wires with increasing deviation from parabolic confinement

We investigate the evolution of the interaction of the magnetoplasmon
resonance with the harmonics of the cyclotron resonance as the confinement of
an electron gas in a quantum wire increasingly deviates from the parabolic
case. The occurrence of the Bernstein modes is observed in a time-dependent
Hartree model of a two-dimensional electron gas in a single quantum wire.Comment: 9 pages, 4 figures, uses IOP macros, to appear in the Journal of
Physics: Condensed Matte

### Far-Infrared Excitations below the Kohn Mode: Internal Motion in a Quantum Dot

We have investigated the far-infrared response of quantum dots in modulation
doped GaAs heterostructures. We observe novel modes at frequencies below the
center-of-mass Kohn mode. Comparison with Hartree-RPA calculations show that
these modes arise from the flattened potential in our field-effect confined
quantum dots. They reflect pronounced relative motion of the charge density
with respect to the center-of-mass.Comment: 8 pages, LaTeX with integrated 6 PostScript figure

### Magnetotransport in a double quantum wire: Modeling using a scattering formalism built on the Lippmann-Schwinger equation

We model electronic transport through a double quantum wire in an external
homogeneous perpendicular magnetic field using a scattering formalism built on
the Lippmann-Schwinger equation. In the scattering region a window is opened
between the parallel wires allowing for inter- and intra-wire scattering
processes. Due to the parity breaking of the magnetic field the ensuing subband
energy spectrum of the double wire system with its regimes of hole- and
electron-like propagating modes leads to a more structure rich conductance as a
function of the energy of the incoming waves than is seen in a single
parabolically confined quantum wire. The more complex structure of the
evanescent modes of the system also leaves its marks on the conductance.Comment: RevTeX, 8 pages with 10 included postscript figures, high resolution
version available at http://hartree.raunvis.hi.is/~vidar/Rann/DW_VGCST_06.pd

### Influence of shape of quantum dots on their far-infrared absorption

We investigate the effects of the shape of quantum dots on their far-infrared
absorption in an external magnetic field by a model calculation. We focus our
attention on dots with a parabolic confinement potential deviating from the
common circular symmetry, and dots having circular doughnut shape. For a
confinement where the generalized Kohn theorem does not hold we are able to
interprete the results in terms of a mixture of a center-of-mass mode and
collective modes reflecting an excitation of relative motion of the electrons.
The calculations are performed within the time-dependent Hartree approximation
and the results are compared to available experimental results.Comment: RevTeX, 16 pages with 10 postscript figures included. Submitted to
Phys. Rev.

### Spin effects in a confined 2DEG: Enhancement of the g-factor, spin-inversion states and their far-infrared absorption

We investigate several spin-related phenomena in a confined two-dimensional
electron gas (2DEG) using the Hartree-Fock approximation for the mutual Coulomb
interaction of the electrons. The exchange term of the interaction causes a
large splitting of the spin levels whenever the chemical potential lies within
a Landau band (LB). This splitting can be reinterpreted as an enhancement of an
effective g-factor, g*. The increase of g* when a LB is half filled can be
accompanied by a spontaneous formation of a static spin-inversion state (SIS)
whose details depend on the system sision state (SIS) whose details depend on
the system size. The coupling of the states of higher LB's into the lowest band
by the Coulomb interaction of the 2DEG is essential for the SIS to occur. The
far-infrared absorption of the system, relatively insensitive to the spin
splitting, develops clear signs of the SIS.Comment: 7 figure

### Manifestation of the magnetic depopulation of one-dimensional subbands in the optical absorption of acoustic magnetoplasmons in side-gated quantum wires

We have investigated experimentally and theoretically the far-infrared (FIR)
absorption of gated, deep-mesa-etched GaAs/Al$_x$Ga$_{1-x}$As quantum wires. To
overcome Kohn's theorem we have in particular prepared double-layered wires and
studied the acoustic magnetoplasmon branch. We find oscillations in the
magnetic-field dispersion of the acoustic plasmon which are traced back to the
self-consistently screened density profile in its dependence on the magnetic
depopulation of the one-dimensional subbands.Comment: LaTeX-file, 4 pages with 3 included ps-figures, to appear in Physica

### Magnetization in short-period mesoscopic electron systems

We calculate the magnetization of the two-dimensional electron gas in a
short-period lateral superlattice, with the Coulomb interaction included in
Hartree and Hartree-Fock approximations. We compare the results for a finite,
mesoscopic system modulated by a periodic potential, with the results for the
infinite periodic system. In addition to the expected strong exchange effects,
the size of the system, the type and the strength of the lateral modulation
leave their fingerprints on the magnetization.Comment: RevTeX4, 10 pages with 14 included postscript figures To be published
in PRB. Replaced to repair figure

### Spin Hot Spots in vertically-coupled Few-electron Quantum Dots

The effects of spin-orbit (SO) coupling arising from the confinement
potential in single and two vertically-coupled quantum dots have been
investigated. Our work indicates that a dot containing a single electron shows
the lifting of the degeneracy of dipole-allowed transitions at B=0 due to the
SO coupling which disappears for a dot containing two electrons. For coupled
dots with one electron in each dot, the optical spectra is not affected by the
coupling and is the same as the dot containing one electron. However, for the
case of two coupled dots where one partner dot has two interacting electrons
while the other dot has only one electron, a remarkable effect is observed
where the oscillator strength of two out of four dipole-allowed transition
lines disappears as the distance between the dots is decreased

- â€¦