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@PHDTHESIS{Gbbels:464464,
author = {Göbbels, Stefan},
othercontributors = {Güntherodt, Gernot and Stampfer, Christoph},
title = {{M}agneto-optische {U}ntersuchungen des elektrisch
induzierten {S}pintransports und des {L}aser-induzierten
{S}pin-{S}eebeck-{T}ransports in n-{G}a{A}s},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {Publikationsserver der RWTH Aachen University},
reportid = {RWTH-2015-01302},
pages = {VII, 141 S. : Ill., graph. Darst.},
year = {2015},
note = {Aachen, Techn. Hochsch., Diss., 2015},
abstract = {The topic of this Ph.D. thesis is the magneto-optical
investigation of the electrically-induced spin transport and
of the laser-induced spin Seebeck transport in n-GaAs. This
work is part of the research project "Spin Caloritronics in
III-V-Semiconductors" of the DFG priority programm "Spin
Caloric Transport" (SPP 1538).Measurements are performed by
spatially and time-resolved Faraday spectroscopy. Here, a
local spin polarisation is generated by ultrafast laser
pulses and detected via the magneto-optical Faraday effect
with variable time delay. The material system under
investigation, i.e. n-GaAs doped to the metal-to-insulator
transition at $n = 2 \cdot 10^{16}$ cm$^{-3}$, is optimally
suited for spin transport experiments due to long spin
dephasing times $\tau_s \geq 100$ ns at low temperatures,
which result in large spin transport length of $\sim
10\,\mu$m.The measurement and analysis method used in this
work allows to study the temporal evolution of the optically
generated spin polarisation by Fourier transformation of
spatially resolved magnetic field scans (RSA scans) with
very high spatial resolution and to determine the spin drift
velocity $v_s$, the spin diffusion constant $D_s$ and the
spin dephasing time $\tau_s$.Spin transport in an applied
electric field shows Ohmic transport behaviour $v_s = -
\mu_s E$ with spin mobility $\mu_s = (1159 \pm 4)$ cm
V$^{-1}$ s$^{-1}$ at $T = 10$ K. Spin transport measurements
in dependence of the excitation energy and of the excitation
density indicate that, under intense excitation at low
temperatures, spin drift and diffusion are influenced by a
strong electron-hole interaction. The temperature dependence
of the electrically-induced spin transport shows the first
experimental verification of the generalized Einstein
relation for semiconductors at the metal-to-insulator
transition at low temperatures.Spin Seebeck transport in
n-GaAs is investigated with laser-induced temperature
gradients, which are characterized by photoluminescence
measurements. While the spin diffusion constant $D_s$ and
the spin dephasing time $\tau_s$ seem to be dominantly
influenced by the large, optically excited electron and hole
density, the spin drift velocity $v_s$ shows the expected
behaviour for spin Seebeck transport in laser-induced
temperature gradients in all the measurements. Particularly,
the simultaneous vanishing of $v_s$ and of the temperature
gradient $\frac{dT}{dx}$ at a lattice temperature of $T =
30$ K confirms the conclusion that these experiments show
the first evidence of lateral spin Seebeck transport in a
non-magnetic semiconductor.},
cin = {132110 / 130000},
ddc = {530},
cid = {$I:(DE-82)132110_20140620$ / $I:(DE-82)130000_20140620$},
typ = {PUB:(DE-HGF)11},
urn = {urn:nbn:de:hbz:82-rwth-2015-013022},
url = {https://publications.rwth-aachen.de/record/464464},
}
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