4,733 research outputs found
Optical polarization of localized hole spins in p-doped quantum wells
The initialization of spin polarization in localized hole states is
investigated using time-resolved Kerr rotation. We find that the sign of the
polarization depends on the magnetic field, and the power and the wavelength of
the circularly polarized pump pulse. An analysis of the spin dynamics and the
spin-initialization process shows that two mechanisms are responsible for spin
polarization with opposite sign: The difference of the g factor between the
localized holes and the trions, as well as the capturing process of dark
excitons by the localized hole states.Comment: 4 pages, 2 figure
Hybrid Quantum Dot-2D Electron Gas Devices for Coherent Optoelectronics
We present an inverted GaAs 2D electron gas with self-assembled InAs quantum
dots in close proximity, with the goal of combining quantum transport with
quantum optics experiments. We have grown and characterized several wafers --
using transport, AFM and optics -- finding narrow-linewidth optical dots and
high-mobility, single subband 2D gases. Despite being buried 500 nm below the
surface, the dots are clearly visible on AFM scans, allowing precise
localization and paving the way towards a hybrid quantum system integrating
optical dots with surface gate-defined nanostructures in the 2D gas.Comment: 4 pages, 5 figures (color
Efficient quantum dot single photon extraction into an optical fiber using a nanophotonic directional coupler
We demonstrate a spectrally broadband and effcient technique for collecting
photoluminescence from a single InAs quantum dot directly into a standard
single mode optical fiber. In this approach, an optical fiber taper waveguide
is placed in contact with a suspended GaAs nanophotonic waveguide with embedded
quantum dots, forming an effcient and broadband directional coupler with
standard optical fiber input and output. Effcient photoluminescence collection
over a wavelength range of tens of nanometers is demonstrated, and a maximum
collection effciency of 6.05 % (corresponding single photon rate of 3.0 MHz)
into a single mode optical fiber was estimated for a single quantum dot
exciton
Drift mobility of long-living excitons in coupled GaAs quantum wells
We observe high-mobility transport of indirect excitons in coupled GaAs
quantum wells. A voltage-tunable in-plane potential gradient is defined for
excitons by exploiting the quantum confined Stark effect in combination with a
lithographically designed resistive top gate. Excitonic photoluminescence
resolved in space, energy, and time provides insight into the in-plane drift
dynamics. Across several hundreds of microns an excitonic mobility of >10^5
cm2/eVs is observed for temperatures below 10 K. With increasing temperature
the excitonic mobility decreases due to exciton-phonon scattering.Comment: 3 pages, 3 figure
Magnetoresistance Induced by Rare Strong Scatterers in a High Mobility 2DEG
We observe a strong negative magnetoresistance at non-quantizing magnetic
fields in a high-mobility two-dimensional electron gas (2DEG). This strong
negative magnetoresistance consists of a narrow peak around zero magnetic field
and a huge magnetoresistance at larger fields. The peak shows parabolic
magnetic field dependence and is attributed to the interplay of smooth disorder
and rare strong scatterers. We identify the rare strong scatterers as
macroscopic defects in the material and determine their density from the peak
curvature.Comment: 5 pages, 4 figure
Spin-sensitive Bleaching and Spin-Relaxation in QW's
Spin-sensitive saturation of absorption of infrared radiation has been
investigated in p-type GaAs QWs. It is shown that the absorption saturation of
circularly polarized radiation is mostly controlled by the spin relaxation time
of the holes. The saturation behavior has been investigated for different QW
widths and in dependence on the temperature with the result that the saturation
intensity substantially decreases with narrowing of QWs. Spin relaxation times
were experimentally obtained by making use of calculated (linear) absorption
coefficients for inter-subband transitions
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