90 research outputs found
Nuclear spin warm-up in bulk n-GaAs
We show that the spin-lattice relaxation in n-type insulating GaAs is
dramatically accelerated at low magnetic fields. The origin of this effect,
that cannot be explained in terms of well-known diffusion-limited hyperfine
relaxation, is found in the quadrupole relaxation, induced by fluctuating donor
charges. Therefore, quadrupole relaxation, that governs low field nuclear spin
relaxation in semiconductor quantum dots, but was so far supposed to be
harmless to bulk nuclei spins in the absence of optical pumping can be studied
and harnessed in much simpler model environment of n-GaAs bulk crystal.Comment: 5 pages, 4 figure
Manipulation of the Spin Memory of Electrons in n-GaAs
We report on the optical manipulation of the electron spin relaxation time in
a GaAs based heterostructure. Experimental and theoretical study shows that the
average electron spin relaxes through hyperfine interaction with the lattice
nuclei, and that the rate can be controlled by the electron-electron
interactions. This time has been changed from 300 ns down to 5 ns by variation
of the laser frequency. This modification originates in the optically induced
depletion of n-GaAs layer
Stabilizing effect of nuclear quadrupole interaction on the polarization of electron-nuclear spin system in a quantum dot
Nuclear quadrupole interaction extends the limits imposed by hyperfine
interaction on the spin coherence of the electron and nuclei in a quantum dot.
The strain-induced nuclear quadrupole interaction suppresses the nuclear spin
flip and makes possible the zero-field dynamic nuclear polarization in
self-organized InP/InGaP quantum dots. The direction of the effective nuclear
magnetic field is fixed in space, thus quenching the magnetic depolarization of
the electron spin in the quantum dot. The quadrupole interaction suppresses the
zero-field electron spin decoherence also for the case of non-polarized nuclei.
These results provide a new vision of the role of the nuclear quadrupole
interaction in nanostructures: it elongates the spin memory of the
electron-nuclear system.Comment: 18 pages including 3 figures. Shortened version has been accepted for
publication in Physical Review Letter
Suppression of electron spin relaxation in Mn-doped GaAs
We report a surprisingly long spin relaxation time of electrons in Mn-doped
p-GaAs. The spin relaxation time scales with the optical pumping and increases
from 12 ns in the dark to 160 ns upon saturation. This behavior is associated
with the difference in spin relaxation rates of electrons precessing in the
fluctuating fields of ionized or neutral Mn acceptors, respectively. For the
latter the antiferromagnetic exchange interaction between a Mn ion and a bound
hole results in a partial compensation of these fluctuating fields, leading to
the enhanced spin memory.Comment: 4 pages, 4 figure
Low-temperature spin relaxation in n-type GaAs
Low-temperature electron spin relaxation is studied by the optical
orientation method in bulk n-GaAs with donor concentrations from 10^14 cm^{-3}
to 5x10^17 cm^{-3}.
A peculiarity related to the metal-to-insulator transition (MIT) is observed
in the dependence of the spin lifetime on doping near n_D = 2x10^16 cm^{-3}. In
the metallic phase, spin relaxation is governed by the Dyakonov-Perel
mechanism, while in the insulator phase it is due to anisotropic exchange
interaction and hyperfine interactio
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
Spin dynamics of electrons and holes in InGaAs/GaAs quantum wells at milliKelvin temperatures
The carrier spin dynamics in a n-doped (In,Ga)As/GaAs quantum well has been
studied by time-resolved Faraday rotation and ellipticity techniques in the
temperature range down to 430 milliKelvin. These techniques give data with very
different spectral dependencies, from which nonetheless consistent information
on the spin dynamics can be obtained, in agreement with theoretical
predictions. The mechanisms of long-lived spin coherence generation are
discussed for the cases of trion and exciton resonant excitation. We
demonstrate that carrier localization leads to a saturation of spin relaxation
times at 45 ns for electrons below 4.5 K and at 2 ns for holes below 2.3 K. The
underlying spin relaxation mechanisms are discussed.Comment: 8 pages, 8 figure
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