192 research outputs found
Magnetoexcitons in quantum-ring structures: a novel magnetic interference effect
A novel magnetic interference effect is proposed for a neutral, but
polarizable exciton in a quantum ring with a finite width. The magnetic
interference effect originates from the nonzero dipole moment in the exciton.
The ground state of exciton acquires a nonzero angular momentum with increasing
normal magnetic field. This leads to the suppression of the photoluminescence
in defined windows of the magnetic field.Comment: 6 pages, 2 figures, Proceed. EP2DS, 2001 (Physica E
Coulomb interactions in single, charged self-assembled quantum dots: radiative lifetime and recombination energy
We present results on the charge dependence of the radiative recombination
lifetime, Tau, and the emission energy of excitons confined to single
self-assembled InGaAs quantum dots. There are significant dot-to-dot
fluctuations in the lifetimes for a particular emission energy. To reach
general conclusions, we present the statistical behavior by analyzing data
recorded on a large number of individual quantum dots. Exciton charge is
controlled with extremely high fidelity through an n-type field effect
structure, providing access to the neutral exciton (X0), the biexciton (2X0)
and the positively (X1+) and negatively (X1-) charged excitons. We find
significant differences in the recombination lifetime of each exciton such
that, on average, Tau(X1-) / Tau(X0) = 1.25, Tau(X1+) / Tau(X0) = 1.58 and
Tau(2X0) / Tau(X0) = 0.65. We attribute the change in lifetime to significant
changes in the single particle hole wave function on charging the dot, an
effect more pronounced on charging X0 with a single hole than with a single
electron. We verify this interpretation by recasting the experimental data on
exciton energies in terms of Coulomb energies. We show directly that the
electron-hole Coulomb energy is charge dependent, reducing in value by 5-10% in
the presence of an additional electron, and that the electron-electron and
hole-hole Coulomb energies are almost equal.Comment: 8 pages, 7 figures, submitted to Phys. Rev.
Voltage-controlled electron-hole interaction in a single quantum dot
The ground state of neutral and negatively charged excitons confined to a
single self-assembled InGaAs quantum dot is probed in a direct absorption
experiment by high resolution laser spectroscopy. We show how the anisotropic
electron-hole exchange interaction depends on the exciton charge and
demonstrate how the interaction can be switched on and off with a small dc
voltage. Furthermore, we report polarization sensitive analysis of the
excitonic interband transition in a single quantum dot as a function of charge
with and without magnetic field.Comment: Conference Proceedings, Physics and Applications of Spin-Related
Phenomena in Semiconductors, Santa Barbara (CA), 2004. 4 pages, 4 figures;
content as publishe
Nanoscale magnetic field mapping with a single spin scanning probe magnetometer
We demonstrate quantitative magnetic field mapping with nanoscale resolution,
by applying a lock-in technique on the electron spin resonance frequency of a
single nitrogen-vacancy defect placed at the apex of an atomic force microscope
tip. In addition, we report an all-optical magnetic imaging technique which is
sensitive to large off-axis magnetic fields, thus extending the operation range
of diamond-based magnetometry. Both techniques are illustrated by using a
magnetic hard disk as a test sample. Owing to the non-perturbing and
quantitative nature of the magnetic probe, this work should open up numerous
perspectives in nanomagnetism and spintronics
Low-temperature, in situ tunable, uniaxial stress measurements in semiconductors using a piezoelectric actuator
We demonstrate the use of a piezoelectric actuator to apply, at low
temperatures, uniaxial stress in the plane of a two-dimensional electron system
confined to a modulation-doped AlAs quantum well. Via the application of
stress, which can be tuned in situ and continuously, we control the energies
and occupations of the conduction-band minima and the electronic properties of
the electron system. We also report measurements of the longitudinal and
transverse strain versus bias for the actuator at 300, 77, and 4.2 K. A
pronounced hysteresis is observed at 300 and 77 K, while at 4.2 K, strain is
nearly linear and shows very little hysteresis with the applied bias.Comment: 2 figure
Cavity cooling of a nanomechanical resonator by light scattering
We present a novel method for opto-mechanical cooling of sub-wavelength sized
nanomechanical resonators. Our scheme uses a high finesse Fabry-Perot cavity of
small mode volume, within which the nanoresonator is acting as a
position-dependant perturbation by scattering. In return, the back-action
induced by the cavity affects the nanoresonator dynamics and can cool its
fluctuations. We investigate such cavity cooling by scattering for a nanorod
structure and predict that ground-state cooling is within reach.Comment: 4 pages, 3 figure
Absorption and photoluminescence spectroscopy on a single self-assembled charge-tunable quantum dot
We have performed detailed photoluminescence (PL) and absorption spectroscopy
on the same single self-assembled quantum dot in a charge-tunable device. The
transition from neutral to charged exciton in the PL occurs at a more negative
voltage than the corresponding transition in absorption. We have developed a
model of the Coulomb blockade to account for this observation. At large
negative bias, the absorption broadens as a result of electron and hole
tunneling. We observe resonant features in this regime whenever the quantum dot
hole level is resonant with two-dimensional hole states located at the capping
layer-blocking barrier interface in our structure.Comment: 6 pages, 6 figure
Dressed excitonic states and quantum interference in a three-level quantum dot ladder system
We observe dressed states and quantum interference effects in a strongly
driven three-level quantum dot ladder system. The effect of a strong coupling
field on one dipole transition is measured by a weak probe field on the second
dipole transition using differential reflection. When the coupling energy is
much larger than both the homoge-neous and inhomogeneous linewidths an
Autler-Townes splitting is observed. Striking differences are observed when the
transitions resonant with the strong and weak fields are swapped, particularly
when the coupling energy is nearly equal to the measured linewidth. This result
is attributed to quantum interference: a modest destructive or constructive
interference is observed depending on the pump / probe geometry. The data
demonstrate that coher-ence of both the bi-exciton and the exciton is
maintained in this solid-state system, even under intense illumina-tion, which
is crucial for prospects in quantum information processing and non-linear
optical devices.Comment: 8 pages, 6 figures, submitted to New Journal of Physic
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