5 research outputs found
Hole spin relaxation in intrinsic and -type bulk GaAs
We investigate hole spin relaxation in intrinsic and -type bulk GaAs from
a fully microscopic kinetic spin Bloch equation approach. In contrast to the
previous study on hole spin dynamics, we explicitly include the intraband
coherence and the nonpolar hole-optical-phonon interaction, both of which are
demonstrated to be of great importance to the hole spin relaxation. The
relative contributions of the D'yakonov-Perel' and Elliott-Yafet mechanisms on
hole spin relaxation are also analyzed. In our calculation, the screening
constant, playing an important role in the hole spin relaxation, is treated
with the random phase approximation. In intrinsic GaAs, our result shows good
agreement with the experiment data at room temperature, where the hole spin
relaxation is demonstrated to be dominated by the Elliott-Yafet mechanism. We
also find that the hole spin relaxation strongly depends on the temperature and
predict a valley in the density dependence of the hole spin relaxation time at
low temperature due to the hole-electron scattering. In -type GaAs, we
predict a peak in the spin relaxation time against the hole density at low
temperature, which originates from the distinct behaviors of the screening in
the degenerate and nondegenerate regimes. The competition between the screening
and the momentum exchange during scattering events can also lead to a valley in
the density dependence of the hole spin relaxation time in the low density
regime. At high temperature, the effect of the screening is suppressed due to
the small screening constant. Moreover, we predict a nonmonotonic dependence of
the hole spin relaxation time on temperature associated with the screening
together with the hole-phonon scattering. Finally, we find that the
D'yakonov-Perel' mechanism can markedly contribute to the .... (omitted due to
the limit of space)Comment: 11 pages, 7 figures, Phys. Rev. B, in pres
Spin relaxation in -type ZnO quantum wells
We perform an investigation on the spin relaxation for -type ZnO (0001)
quantum wells by numerically solving the kinetic spin Bloch equations with all
the relevant scattering explicitly included. We show the temperature and
electron density dependence of the spin relaxation time under various
conditions such as impurity density, well width, and external electric field.
We find a peak in the temperature dependence of the spin relaxation time at low
impurity density. This peak can survive even at 100 K, much higher than the
prediction and measurement value in GaAs. There also exhibits a peak in the
electron density dependence at low temperature. These two peaks originate from
the nonmonotonic temperature and electron density dependence of the Coulomb
scattering. The spin relaxation time can reach the order of nanosecond at low
temperature and high impurity density.Comment: 6 pages, 4 figure
Hole spin relaxation in [001] strained asymmetric Si/SiGe and Ge/SiGe quantum wells
Hole spin relaxation in [001] strained asymmetric Si/SiGe
(Ge/SiGe) quantum wells is investigated in the situation with
only the lowest hole subband being relevant. The effective Hamiltonian of the
lowest hole subband is obtained by the subband L\"owdin perturbation method in
the framework of the six-band Luttinger model, with
sufficient basis functions included. The lowest hole subband in Si/SiGe quantum
wells is light-hole like with the Rashba spin-orbit coupling term depending on
momentum both linearly and cubically, while that in Ge/SiGe quantum wells is a
heavy hole state with the Rashba spin-orbit coupling term depending on momentum
only cubically. The hole spin relaxation is investigated by means of the fully
microscopic kinetic spin Bloch equation approach, with all the relevant
scatterings considered. It is found that the hole-phonon scattering is very
weak, which makes the hole-hole Coulomb scattering become very important. The
hole system in Si/SiGe quantum wells is generally in the strong scattering
limit, while that in Ge/SiGe quantum wells can be in either the strong or the
weak scattering limit. The Coulomb scattering leads to a peak in both the
temperature and hole density dependences of spin relaxation time in Si/SiGe
quantum wells, located around the crossover between the degenerate and
nondegenerate regimes. Nevertheless, the Coulomb scattering leads to not only a
peak but also a valley in the temperature dependence of spin relaxation time in
Ge/SiGe quantum wells.... (The remaining is omitted due to the limit of space).Comment: 12 pages, 11 figures, PRB in pres
Electron spin relaxation in bulk III-V semiconductors from a fully microscopic kinetic spin Bloch equation approach
Electron spin relaxation in bulk III-V semiconductors is investigated from a
fully microscopic kinetic spin Bloch equation approach where all relevant
scatterings, such as, the electron--nonmagnetic-impurity, electron-phonon,
electron-electron, electron-hole, and electron-hole exchange (the
Bir-Aronov-Pikus mechanism) scatterings are explicitly included. The
Elliot-Yafet mechanism is also fully incorporated. This approach offers a way
toward thorough understanding of electron spin relaxation both near and far
away from the equilibrium in the metallic regime. The dependence of the spin
relaxation time on electron density, temperature, initial spin polarization,
photo-excitation density, and hole density are studied thoroughly with the
underlying physics analyzed. In contrast to the previous investigations in the
literature, we find that: (i) In -type materials, the Elliot-Yafet mechanism
is {\em less} important than the D'yakonov-Perel' mechanism, even for the
narrow band-gap semiconductors such as InSb and InAs. (ii) The density
dependence of the spin relaxation time is nonmonotonic and we predict a {\em
peak} in the metallic regime in both -type and intrinsic materials. (iii) In
intrinsic materials, the Bir-Aronov-Pikus mechanism is found to be negligible
compared with the D'yakonov-Perel' mechanism. We also predict a peak in the
temperature dependence of spin relaxation time which is due to the nonmonotonic
temperature dependence of the electron-electron Coulomb scattering in intrinsic
materials with small initial spin polarization. (iv) In -type III-V
semiconductors, ...... (the remaining is omitted here due to the limit of
space)Comment: 25 pages, 17 figure