24 research outputs found
Ultimate photo-induced Kerr rotation achieved in semiconductor microcavities
Photoinduced Kerr rotation by more than radians is demonstrated in
planar quantum well microcavity in the strong coupling regime. This result is
close to the predicted theoretical maximum of . It is achieved by
engineering microcavity parameters such that the optical impedance matching
condition is reached at the smallest negative detuning between exciton
resonance and the cavity mode. This ensures the optimum combination of the
exciton induced optical non-linearity and the enhancement of the Kerr angle by
the cavity. Comprehensive analysis of the polarization state of the light in
this regime shows that both renormalization of the exciton energy and the
saturation of the excitonic resonance contribute to the observed optical
nonlinearities.Comment: Shortened version prepared to submit in Phys. Rev. Letter
Local field of spin-spin interactions in the nuclear spin system of n-GaAs
At low lattice temperatures the nuclear spins in a solid form a closed
thermodynamic system that is well isolated from the lattice. Thermodynamic
properties of the nuclear spin system are characterized by the local field of
spin-spin interactions, which determines its heat capacity and the minimal
achievable nuclear spin temperature in demagnetization experiments. We report
the results of measurement of the local field for the nuclear spin system in
GaAs, which is a model material for semiconductor spintronics. The choice of
the structure, a weakly doped GaAs epitaxial layer with weak residual
deformations, and of the measurement method, the adiabatic demagnetization of
optically cooled nuclear spins, allowed us to refine the value of nuclear
spin-spin local field, which turned out to be two times less than one
previously obtained. Our experimental results are confirmed by calculations,
which take into account dipole-dipole and indirect (pseudodipolar and exchange)
nuclear spin interactions.Comment: 23 pages, 6 figures, 1 tabl
Nuclear spin-lattice relaxation in p-type GaAs
Spin-lattice relaxation of the nuclear spin system in p-type GaAs is studied
using a three-stage experimental protocol including optical pumping and
measuring the difference of the nuclear spin polarization before and after a
dark interval of variable length. This method allows us to measure the
spin-lattice relaxation time of optically pumped nuclei "in the dark",
that is, in the absence of illumination. The measured values fall into
the sub-second time range, being three orders of magnitude shorter than in
earlier studied n-type GaAs. The drastic difference is further emphasized by
magnetic-field and temperature dependences of in p-GaAs, showing no
similarity to those in n-GaAs. This unexpected behavior is explained within a
developed theoretical model involving quadrupole relaxation of nuclear spins,
which is induced by electric fields within closely spaced donor-acceptor pairs.Comment: 9 pages, 8 figure
Optics of spin-noise-induced gyrotropy of asymmetric microcavity
The optical gyrotropy noise of a high-finesse semiconductor Bragg microcavity
with an embedded quantum well (QW) is studied at different detunings of the
photon mode and the QW exciton resonances. A strong suppression of the noise
magnitude for the photon mode frequencies lying above exciton resonances is
found. We show that such a critical behavior of the observed optical noise
power is specific of asymmetric Fabry-Perot resonators. As follows from our
analysis, at a certain level of intracavity loss, the reflectivity of the
asymmetric resonator vanishes, while the polarimetric sensitivity to the
gyrotropy changes dramatically when moving across the critical point. The
results of model calculations are in a good agreement with our experimental
data on the spin noise in a single-quantum-well microcavity and are confirmed
also by the spectra of the photo-induced Kerr rotation in the pump-probe
experiments.Comment: 6 pages, 5 figure
High resolution nuclear magnetic resonance spectroscopy of highly-strained quantum dot nanostructures
Much new solid state technology for single-photon sources, detectors,
photovoltaics and quantum computation relies on the fabrication of strained
semiconductor nanostructures. Successful development of these devices depends
strongly on techniques allowing structural analysis on the nanometer scale.
However, commonly used microscopy methods are destructive, leading to the loss
of the important link between the obtained structural information and the
electronic and optical properties of the device. Alternative non-invasive
techniques such as optically detected nuclear magnetic resonance (ODNMR) so far
proved difficult in semiconductor nano-structures due to significant
strain-induced quadrupole broadening of the NMR spectra. Here, we develop new
high sensitivity techniques that move ODNMR to a new regime, allowing high
resolution spectroscopy of as few as 100000 quadrupole nuclear spins. By
applying these techniques to individual strained self-assembled quantum dots,
we measure strain distribution and chemical composition in the volume occupied
by the confined electron. Furthermore, strain-induced spectral broadening is
found to lead to suppression of nuclear spin magnetization fluctuations thus
extending spin coherence times. The new ODNMR methods have potential to be
applied for non-invasive investigations of a wide range of materials beyond
single nano-structures, as well as address the task of understanding and
control of nuclear spins on the nanoscale, one of the central problems in
quantum information processing