928 research outputs found
Carbon-doped high mobility two-dimensional hole gases on (110) faced GaAs
Carbon-doped high mobility two-dimensional hole gases grown on (110) oriented
GaAs substrates have been grown with hole mobilities exceeding 10^6 cm^2/Vs in
single heterojunction GaAs/AlGaAs structures. At these high mobilities, a
pronounced mobility anisotropy has been observed. Rashba induced spin-splitting
in these asymmetric structures has been found to be independent on the
transport direction
Carbon doped symmetric GaAs/AlGaAs quantum wells with hole mobilities beyond 10^6 cm^2/Vs
Utilizing a novel carbon doping source, we prepared two-dimensional hole
gases in a symmetric quantum well structure in the GaAs/AlGaAs heterosystem.
Low temperature hole mobilities up to 1.2 x 10^6 cm^2/Vs at a density of 2.3 x
10^11 cm^-2 were achieved on GaAs (001) substrates. In contrast to electron
systems, the hole mobility sensitively depends on variations of the quantum
well width and the spacer thickness. In particular an increase of the quantum
well width from an optimal value of 15 nm to 18 nm is accompanied by a 35 %
reduction of the hole mobility. The quality of ultrahigh-mobility electron
systems is not affected by the employed carbon doping source
Gate control of low-temperature spin dynamics in two-dimensional hole systems
We have investigated spin and carrier dynamics of resident holes in
high-mobility two-dimensional hole systems in GaAs/AlGaAs
single quantum wells at temperatures down to 400 mK. Time-resolved Faraday and
Kerr rotation, as well as time-resolved photoluminescence spectroscopy are
utilized in our study. We observe long-lived hole spin dynamics that are
strongly temperature dependent, indicating that in-plane localization is
crucial for hole spin coherence. By applying a gate voltage, we are able to
tune the observed hole g factor by more than 50 percent. Calculations of the
hole g tensor as a function of the applied bias show excellent agreement with
our experimental findings.Comment: 8 pages, 7 figure
Engineering ultralong spin coherence in two-dimensional hole systems at low temperatures
For the realisation of scalable solid-state quantum-bit systems, spins in
semiconductor quantum dots are promising candidates. A key requirement for
quantum logic operations is a sufficiently long coherence time of the spin
system. Recently, hole spins in III-V-based quantum dots were discussed as
alternatives to electron spins, since the hole spin, in contrast to the
electron spin, is not affected by contact hyperfine interaction with the
nuclear spins. Here, we report a breakthrough in the spin coherence times of
hole ensembles, confined in so called natural quantum dots, in narrow
GaAs/AlGaAs quantum wells at temperatures below 500 mK. Consistently,
time-resolved Faraday rotation and resonant spin amplification techniques
deliver hole-spin coherence times, which approach in the low magnetic field
limit values above 70 ns. The optical initialisation of the hole spin
polarisation, as well as the interconnected electron and hole spin dynamics in
our samples are well reproduced using a rate equation model.Comment: 16 pages, 6 figure
Performance of HPGe Detectors in High Magnetic Fields
A new generation of high-resolution hypernuclear gamma$-spectroscopy
experiments with high-purity germanium detectors (HPGe) are presently designed
at the FINUDA spectrometer at DAPhiNE, the Frascati phi-factory, and at PANDA,
the antiproton proton hadron spectrometer at the future FAIR facility. Both,
the FINUDA and PANDA spectrometers are built around the target region covering
a large solid angle. To maximise the detection efficiency the HPGe detectors
have to be located near the target, and therefore they have to be operated in
strong magnetic fields B ~ 1 T. The performance of HPGe detectors in such an
environment has not been well investigated so far. In the present work VEGA and
EUROBALL Cluster HPGe detectors were tested in the field provided by the ALADiN
magnet at GSI. No significant degradation of the energy resolution was found,
and a change in the rise time distribution of the pulses from preamplifiers was
observed. A correlation between rise time and pulse height was observed and is
used to correct the measured energy, recovering the energy resolution almost
completely. Moreover, no problems in the electronics due to the magnetic field
were observed.Comment: submitted to Nucl. Instrum. Meth. Phys. Res. A, LaTeX, 19 pages, 9
figure
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