383 research outputs found
Modeling spin transport in electrostatically-gated lateral-channel silicon devices: role of interfacial spin relaxation
Using a two-dimensional finite-differences scheme to model spin transport in
silicon devices with lateral geometry, we simulate the effects of spin
relaxation at interfacial boundaries, i.e. the exposed top surface and at an
electrostatically-controlled backgate with SiO_2 dielectric. These
gate-voltage-dependent simulations are compared to previous experimental
results and show that strong spin relaxation due to extrinsic effects yield an
Si/SiO_2 interfacial spin lifetime of ~ 1ns, orders of magnitude lower than
lifetimes in the bulk Si, whereas relaxation at the top surface plays no
substantial role. Hall effect measurements on ballistically injected electrons
gated in the transport channel yield the carrier mobility directly and suggest
that this reduction in spin lifetime is only partially due to enhanced
interfacial momentum scattering which induces random spin flips as in the
Elliott effect. Therefore, other extrinsic mechanisms such as those caused by
paramagnetic defects should also be considered in order to explain the dramatic
enhancement in spin relaxation at the gate interface over bulk values
Spin relaxation and decoherence of two-level systems
We revisit the concepts of spin relaxation and spin decoherence of two level
(spin-1/2) systems. From two toy-models, we clarify two issues related to the
spin relaxation and decoherence: 1) For an ensemble of two-level particles each
subjected to a different environmental field, there exists an ensemble
relaxation time which is fundamentally different from . When the
off-diagonal coupling of each particle is in a single mode with the same
frequency but a random coupling strength, we show that is finite while
the spin relaxation time of a single spin and the usual ensemble
decoherence time are infinite. 2) For a two-level particle under only a
random diagonal coupling, its relaxation time shall be infinite but its
decoherence time is finite.Comment: 5 pages, 2 figure
The Larmor clock and anomalous spin dephasing in silicon
Drift-diffusion theory - which fully describes charge transport in
semiconductors - is also universally used to model transport of spin-polarized
electrons in the presence of longitudinal electric fields. By transforming spin
transit time into spin orientation with precession (a technique called the
"Larmor clock") in current-sensing vertical-transport intrinsic Si devices, we
show that spin diffusion (and concomitant spin dephasing) can be greatly
enhanced with respect to charge diffusion, in direct contrast to predictions of
spin Coulomb-drag diffusion suppression.Comment: minor edits and updated ref
Ab initio investigation of Elliott-Yafet electron-phonon mechanism in laser-induced ultrafast demagnetization
The spin-flip (SF) Eliashberg function is calculated from first-principles
for ferromagnetic Ni to accurately establish the contribution of Elliott-Yafet
electron-phonon SF scattering to Ni's femtosecond laser-driven demagnetization.
This is used to compute the SF probability and demagnetization rate for
laser-created thermalized as well as non-equilibrium electron distributions.
Increased SF probabilities are found for thermalized electrons, but the induced
demagnetization rate is extremely small. A larger demagnetization rate is
obtained for {non-equilibrium} electron distributions, but its contribution is
too small to account for femtosecond demagnetization.Comment: 5 pages, 3 figures, to appear in PR
The dominant spin relaxation mechanism in compound organic semiconductors
Despite the recent interest in "organic spintronics", the dominant spin
relaxation mechanism of electrons or holes in an organic compound semiconductor
has not been conclusively identified. There have been sporadic suggestions that
it might be hyperfine interaction caused by background nuclear spins, but no
confirmatory evidence to support this has ever been presented. Here, we report
the electric-field dependence of the spin diffusion length in an organic
spin-valve structure consisting of an Alq3 spacer layer, and argue that this
data, as well as available data on the temperature dependence of this length,
contradict the notion that hyperfine interactions relax spin. Instead, they
suggest that the Elliott-Yafet mechanism, arising from spin-orbit interaction,
is more likely the dominant spin relaxing mechanism.Comment: Accepted for publication in Physical Review
Elliot-Yafet mechanism in graphene
The differences between spin relaxation in graphene and in other materials
are discussed. For relaxation by scattering processes, the Elliot-Yafet
mechanism, the relation between the spin and the momentum scattering times
acquires a dependence on the carrier density, which is independent of the
scattering mechanism and the relation between mobility and carrier
concentration. This dependence puts severe restrictions on the origin of the
spin relaxation in graphene. The density dependence of the spin relaxation
allows us to distinguish between ordinary impurities and defects which modify
locally the spin-orbit interaction.Comment: 4 pages + \epsilon + S
Surface spin flip probability of mesoscopic Ag wires
Spin relaxation in mesoscopic Ag wires in the diffusive transport regime is
studied via nonlocal spin valve and Hanle effect measurements performed on
permalloy/Ag lateral spin valves. The ratio between momentum and spin
relaxation times is not constant at low temperatures. This can be explained
with the Elliott-Yafet spin relaxation mechanism by considering the momentum
surface relaxation time as being temperature dependent. We present a model to
separately determine spin flip probabilities for phonon, impurity and surface
scattering and find that the spin flip probability is highest for surface
scattering.Comment: 5 pages, 4 figure
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