173 research outputs found
Quantum size effects on spin-tunneling time in a magnetic resonant tunneling diode
We study theoretically the quantum size effects of a magnetic resonant
tunneling diode (RTD) with a (Zn,Mn)Se dilute magnetic semiconductor layer on
the spin-tunneling time and the spin polarization of the electrons. The results
show that the spin-tunneling times may oscillate and a great difference between
the tunneling time of the electrons with opposite spin directions can be
obtained depending on the system parameters. We also study the effect of
structural asymmetry which is related to the difference in the thickness of the
nonmagnetic layers. It is found that the structural asymmetry can greatly
affect the traversal time and the spin polarization of the electrons tunneling
through the magnetic RTD. The results indicate that, by choosing suitable
values for the thickness of the layers, one can design a high speed and perfect
spin-filter diode.Comment: 6 pages, 5 figure
Detection of electrical spin injection by light-emitting diodes in top- and side-emission configuration
Detection of the degree of circular polarization of the electroluminescence
of a light-emitting diode fitted with a spin injecting contact (a spin-LED)
allows for a direct determination of the spin polarization of the injected
carriers. Here, we compare the detection efficiency of (Al,Ga)As spin-LEDs
fitted with a (Zn,Be,Mn)Se spin injector in top- and side-emission
configuration. In contrast with top emission, we cannot detect the electrical
spin injection in side emission from analysing the degree of circular
polarization of the electroluminescence. To reduce resonant optical pumping of
quantum-well excitons in the side emission, we have analysed structures with
mesa sizes as small as 1 micron.Comment: 15 pages with 3 figure
Molecular-beam epitaxy of (Zn,Mn)Se on Si(100)
We have investigated the growth by molecular-beam epitaxy of the II-VI
diluted magnetic semiconductor (Zn,Mn)Se on As-passivated Si(100) substrates.
The growth start has been optimized by using low-temperature epitaxy. Surface
properties were assessed by Nomarski and scanning electron microscopy. Optical
properties of (Zn,Mn)Se have been studied by photoluminescence and a giant
Zeeman splitting of up to 30 meV has been observed. Our observations indicate a
high crystalline quality of the epitaxial films.Comment: To be published in Applied Physics Letter
Spin Current in Spin-Orbit Coupling Systems
We present a simple and pedagogical derivation of the spin current as the
linear response to an external electric field for both Rashba and Luttinger
spin-orbital coupling Hamiltonians. Except for the adiabatic approximation, our
derivation is exact to the linear order of the electric field for both models.
The spin current is a direct result of the difference in occupation levels
between different bands. Moreover, we show a general topological spin current
can be defined for a broad class of spin-orbit coupling systems
Electrical expression of spin accumulation in ferromagnet/semiconductor structures
We treat the spin injection and extraction via a ferromagnetic
metal/semiconductor Schottky barrier as a quantum scattering problem. This
enables the theory to explain a number of phenomena involving spin-dependent
current through the Schottky barrier, especially the counter-intuitive spin
polarization direction in the semiconductor due to current extraction seen in
recent experiments. A possible explanation of this phenomenon involves taking
into account the spin-dependent inelastic scattering via the bound states in
the interface region. The quantum-mechanical treatment of spin transport
through the interface is coupled with the semiclassical description of
transport in the adjoining media, in which we take into account the in-plane
spin diffusion along the interface in the planar geometry used in experiments.
The theory forms the basis of the calculation of spin-dependent current flow in
multi-terminal systems, consisting of a semiconductor channel with many
ferromagnetic contacts attached, in which the spin accumulation created by spin
injection/extraction can be efficiently sensed by electrical means. A
three-terminal system can be used as a magnetic memory cell with the bit of
information encoded in the magnetization of one of the contacts. Using five
terminals we construct a reprogrammable logic gate, in which the logic inputs
and the functionality are encoded in magnetizations of the four terminals,
while the current out of the fifth one gives a result of the operation.Comment: A review to appear in Mod. Phys. Lett.
Coherently photo-induced ferromagnetism in diluted magnetic semiconductors
Ferromagnetism is predicted in undoped diluted magnetic semiconductors
illuminated by intense sub-bandgap laser radiation . The mechanism for
photo-induced ferromagnetism is coherence between conduction and valence bands
induced by the light which leads to an optical exchange interaction. The
ferromagnetic critical temperature T_C depends both on the properties of the
material and on the frequency and intensity of the laser and could be above 1
K.Comment: 11 pages, 2 figures, preprint styl
Probing Spin-Polarized Currents in the Quantum Hall Regime
An experiment to probe spin-polarized currents in the quantum Hall regime is
suggested that takes advantage of the large Zeeman-splitting in the
paramagnetic diluted magnetic semiconductor zinc manganese selenide
(ZnMnSe). In the proposed experiment spin-polarized electrons are
injected by ZnMnSe-contacts into a gallium arsenide (GaAs) two-dimensional
electron gas (2DEG) arranged in a Hall bar geometry. We calculated the
resulting Hall resistance for this experimental setup within the framework of
the Landauer-B\"uttiker formalism. These calculations predict for 100%
spininjection through the ZnMnSe-contacts a Hall resistance twice as high as in
the case of no spin-polarized injection of charge carriers into a 2DEG for
filling factor . We also investigated the influence of the equilibration
of the spin-polarized electrons within the 2DEG on the Hall resistance. In
addition, in our model we expect no coupling between the contact and the 2DEG
for odd filling factors of the 2DEG for 100% spininjection, because of the
opposite sign of the g-factors of ZnMnSe and GaAs.Comment: 7 pages, 5 figure
Electron Spin Injection at a Schottky Contact
We investigate theoretically electrical spin injection at a Schottky contact
between a spin-polarized electrode and a non-magnetic semiconductor. Current
and electron density spin-polarizations are discussed as functions of barrier
energy and semiconductor doping density. The effect of a spin-dependent
interface resistance that results from a tunneling region at the
contact/semiconductor interface is described. The model can serve as a guide
for designing spin-injection experiments with regard to the interface
properties and device structure.Comment: 4 pages, 4 figure
The Rashba Hamiltonian and electron transport
The Rashba Hamiltonian describes the splitting of the conduction band as a
result of spin-orbit coupling in the presence of an external field and is
commonly used to model the electronic structure of confined narrow-gap
semiconductors. Due to the mixing of spin states some care has to be exercised
in the calculation of transport properties. We derive the velocity operator for
the Rashba-split conduction band and demonstrate that the transmission of an
interface between a ferromagnet and a Rashba-split semiconductor does not
depend on the magnetization direction, in contrast with previous assertions in
the literature.Comment: one tex file, two figures; paper to appear in this form in PRB (RC
Optoelectric spin injection in semiconductor heterostructures without ferromagnet
We have shown that electron spin density can be generated by a dc current
flowing across a junction with an embedded asymmetric quantum well. Spin
polarization is created in the quantum well by radiative electron-hole
recombination when the conduction electron momentum distribution is shifted
with respect to the momentum distribution of holes in the spin split valence
subbands. Spin current appears when the spin polarization is injected from the
quantum well into the -doped region of the junction. The accompanied
emission of circularly polarized light from the quantum well can serve as a
spin polarization detector.Comment: 2 figure
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