1,195 research outputs found
Resonant spin amplification of hole spin dynamics in two‐dimensional hole systems: experiment and simulation
Spins in semiconductor structures may allow for the realization of scalable quantum bit arrays, an essential
component for quantum computation schemes. Specifically, hole spins may be more suited for this purpose than electron
spins, due to their strongly reduced interaction with lattice nuclei, which limits spin coherence for electrons in quantum dots.
Here, we present resonant spin amplification (RSA) measurements, performed on a p-modulation doped GaAs-based quantum
well at temperatures below 500 mK. The RSA traces have a peculiar, butterfly-like shape, which stems from the initialization
of a resident hole spin polarization by optical orientation. The combined dynamics of the optically oriented electron and hole
spins are well-described by a rate equation model, and by comparison of experiment and model, hole spin dephasing times of
more than 70 ns are extracted from the measured data
Controlling hole spin dynamics in two‐dimensional hole systems at low temperatures
With the recent discovery of very long hole spin decoherence times in GaAs/AlGaAs heterostructures of more than 70 ns
in two-dimensional hole systems, using the hole spin as a viable alternative to electron spins in spintronic applications seems
possible. Furthermore, as the hyperfine interaction with the nuclear spins is likely to be the limiting factor for electron spin
lifetimes in zero dimensions, holes with their suppressed Fermi contact hyperfine interaction due to their p-like nature should
be able to show even longer lifetimes than electrons. For spintronic applications, electric-field control of hole spin dynamics
is desirable.
Here, we report on time-resolved Kerr rotation and resonant spin amplification measurements on a two-dimensional hole
system in a p-doped GaAs/AlGaAs heterostructure. Via a semitransparent gate, we tune the charge density within the sample.
We are able to observe a change in the hole g factor, as well as in the hole spin dephasing time at high magnetic fields
Electron spin relaxation in paramagnetic Ga(Mn)As quantum wells
Electron spin relaxation in paramagnetic Ga(Mn)As quantum wells is studied
via the fully microscopic kinetic spin Bloch equation approach where all the
scatterings, such as the electron-impurity, electron-phonon, electron-electron
Coulomb, electron-hole Coulomb, electron-hole exchange (the Bir-Aronov-Pikus
mechanism) and the - exchange scatterings, are explicitly included. The
Elliot-Yafet mechanism is also incorporated. From this approach, we study the
spin relaxation in both -type and -type Ga(Mn)As quantum wells. For
-type Ga(Mn)As quantum wells where most Mn ions take the interstitial
positions, we find that the spin relaxation is always dominated by the DP
mechanism in metallic region. Interestingly, the Mn concentration dependence of
the spin relaxation time is nonmonotonic and exhibits a peak. This behavior is
because that the momentum scattering and the inhomogeneous broadening have
different density dependences in the non-degenerate and degenerate regimes. For
-type Ga(Mn)As quantum wells, we find that Mn concentration dependence of
the spin relaxation time is also nonmonotonic and shows a peak. Differently,
this behavior is because that the - exchange scattering (or the
Bir-Aronov-Pikus) mechanism dominates the spin relaxation in the high Mn
concentration regime at low (or high) temperature, whereas the DP mechanism
determines the spin relaxation in the low Mn concentration regime. The
Elliot-Yafet mechanism also contributes the spin relaxation at intermediate
temperature. The spin relaxation time due to the DP mechanism increases with Mn
concentration due to motional narrowing, whereas those due to the spin-flip
mechanisms decrease with Mn concentration, which thus leads to the formation of
the peak.... (The remaining is omitted due to the space limit)Comment: 12 pages, 8 figures, Phys. Rev. B 79, 2009, in pres
Scanning Raman spectroscopy of graphene antidot lattices: Evidence for systematic p-type doping
We have investigated antidot lattices, which were prepared on exfoliated
graphene single layers via electron-beam lithography and ion etching, by means
of scanning Raman spectroscopy. The peak positions, peak widths and intensities
of the characteristic phonon modes of the carbon lattice have been studied
systematically in a series of samples. In the patterned samples, we found a
systematic stiffening of the G band mode, accompanied by a line narrowing,
while the 2D mode energies are found to be linearly correlated with the G mode
energies. We interpret this as evidence for p-type doping of the nanostructured
graphene
Hole spin dynamics and hole factor anisotropy in coupled quantum well systems
Due to its p-like character, the valence band in GaAs-based heterostructures
offers rich and complex spin-dependent phenomena. One manifestation is the
large anisotropy of Zeeman spin splitting. Using undoped, coupled quantum wells
(QWs), we examine this anisotropy by comparing the hole spin dynamics for high-
and low-symmetry crystallographic orientations of the QWs. We directly measure
the hole factor via time-resolved Kerr rotation, and for the low-symmetry
crystallographic orientations (110) and (113a), we observe a large in-plane
anisotropy of the hole factor, in good agreement with our theoretical
calculations. Using resonant spin amplification, we also observe an anisotropy
of the hole spin dephasing in the (110)-grown structure, indicating that
crystal symmetry may be used to control hole spin dynamics
Circularly Polarized Resonant Rayleigh Scattering and Skyrmions in the = 1 Quantum Hall Ferromagnet
We use the circularly polarized resonant Rayleigh scattering (RRS) to study
the quantum Hall ferromagnet at = 1. At this filling factor we observe a
right handed copolarized RRS which probes the Skyrmion spin texture of the
electrons in the photoexcited grounds state. The resonant scattering is not
present in the left handed copolarization, and this can be related to the
correlation between Skymionic effects, screening and spin wave excitations.
These results evidence that RRS is a valid method for the study of the spin
texture of the quantum Hall states
Time-Resolved Studies of a Rolled-Up Semiconductor Microtube Laser
We report on lasing in rolled-up microtube resonators. Time-resolved studies
on these semiconductor lasers containing GaAs quantum wells as optical gain
material reveal particularly fast turn-on-times and short pulse emissions above
the threshold. We observe a strong red-shift of the laser mode during the pulse
emission which is compared to the time evolution of the charge-carrier density
calculated by rate equations
Spin dynamics in p-doped semiconductor nanostructures subject to a magnetic field tilted from the Voigt geometry
We develop a theoretical description of the spin dynamics of resident holes
in a p-doped semiconductor quantum well (QW) subject to a magnetic field tilted
from the Voigt geometry. We find the expressions for the signals measured in
time-resolved Faraday rotation (TRFR) and resonant spin amplification (RSA)
experiments and study their behavior for a range of system parameters. We find
that an inversion of the RSA peaks can occur for long hole spin dephasing times
and tilted magnetic fields. We verify the validity of our theoretical findings
by performing a series of TRFR and RSA experiments on a p-modulation doped
GaAs/Al_{0.3}Ga_{0.7}As single QW and showing that our model can reproduce
experimentally observed signals.Comment: 9 pages, 3 figures; corrected typo
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