935 research outputs found
Highly polarized injection luminescence in forward-biased ferromagnetic-semiconductor junctions at low spin polarization of current
We consider electron tunneling from a nonmagnetic -type semiconductor
(-S) into a ferromagnet (FM) through a very thin forward-biased Schottky
barrier resulting in efficient extraction of electron spin from a thin -S
layer near FM-S interface at low spin polarization of the current. We show that
this effect can be used for an efficient polarization radiation source in a
heterostructure where the accumulated spin polarized electrons are injected
from -S and recombine with holes in a quantum well. The radiation
polarization depends on a bias voltage applied to the FM-S junction.Comment: 4 pages, 2 figure
High-frequency spin valve effect in ferromagnet-semiconductor-ferromagnet structure based on precession of injected spins
New mechanism of magnetoresistance, based on tunneling-emission of spin
polarized electrons from ferromagnets (FM) into semiconductors (S) and
precession of electron spin in the semiconductor layer under external magnetic
field, is described. The FM-S-FM structure is considered, which includes very
thin heavily doped (delta-doped) layers at FM-S interfaces. At certain
parameters the structure is highly sensitive at room-temperature to variations
of the field with frequencies up to 100 GHz. The current oscillates with the
field, and its relative amplitude is determined only by the spin polarizations
of FM-S junctions at relatively large bias voltage.Comment: 5 pages, 2 figures, (v2) new plot with a dependence of current J on
magnetic field H added in Fig.2 (top panel), minor amendments in the text;
(v3) minor typos corrected. To appear in Phys. Rev. Letter
Complete spin polarization of electrons in semiconductor layers and quantum dots
We demonstrate that non-equilibrium electrons in thin nonmagnetic
semiconductor layers or quantum dots can be fully spin polarized by means of
simultaneous electrical spin injection and extraction. The complete spin
polarization is achieved if the thin layers or quantum dots are placed between
two ferromagnetic metal contacts with moderate spin injection coefficients and
antiparallel magnetizations. The sign of the spin polarization is determined by
the direction of the current. Aplications of this effect in spintronics and
quantum information processing are discussed
Spin magnetotransport in two-dimensional hole systems
Spin current of two-dimensional holes occupying the ground-state subband in
an asymmetric quantum well and interacting with static disorder potential is
calculated in the presence of a weak magnetic field H perpendicular to the well
plane. Both spin-orbit coupling and Zeeman coupling are taken into account. It
is shown that the applied electric field excites both the transverse
(spin-Hall) and diagonal spin currents, the latter changes its sign at a finite
H and becomes greater than the spin-Hall current as H increases. The effective
spin-Hall conductivity introduced to describe the spin response in Hall bars is
considerably enhanced by the magnetic field in the case of weak disorder and
demonstrates a non-monotonic dependence on H.Comment: 4 pages, 2 figures, published in Phys. Rev.
Triplet supercurrent in ferromagnetic Josephson junctions by spin injection
We show that injecting nonequilibrium spins into the superconducting leads
strongly enhances the stationary Josephson current through a
superconductor-ferromagnet-superconductor junction. The resulting long-range
super-current through a ferromagnet is carried by triplet Cooper pairs that are
formed in s-wave superconductors by the combined effects of spin injection and
exchange interaction. We quantify the exchange interaction in terms of Landau
Fermi-liquid factors. The magnitude and direction of the long-range Josephson
current can be manipulated by varying the angles of the injected polarizations
with respect to the magnetization in the ferromagnet
Drift-diffusion model for spin-polarized transport in a non-degenerate 2DEG controlled by a spin-orbit interaction
We apply the Wigner function formalism to derive drift-diffusion transport
equations for spin-polarized electrons in a III-V semiconductor single quantum
well. Electron spin dynamics is controlled by the linear in momentum spin-orbit
interaction. In a studied transport regime an electron momentum scattering rate
is appreciably faster than spin dynamics. A set of transport equations is
defined in terms of a particle density, spin density, and respective fluxes.
The developed model allows studying of coherent dynamics of a non-equilibrium
spin polarization. As an example, we consider a stationary transport regime for
a heterostructure grown along the (0, 0, 1) crystallographic direction. Due to
the interplay of the Rashba and Dresselhaus spin-orbit terms spin dynamics
strongly depends on a transport direction. The model is consistent with results
of pulse-probe measurement of spin coherence in strained semiconductor layers.
It can be useful for studying properties of spin-polarized transport and
modeling of spintronic devices operating in the diffusive transport regime.Comment: 16 pages, 3 figure
Multi-subband effect in spin dephasing in semiconductor quantum wells
Multi-subband effect on spin precession and spin dephasing in -type GaAs
quantum wells is studied with electron-electron and electron-phonon scattering
explicitly included. The effects of temperature, well width and applied
electric field (in hot-electron regime) on the spin kinetics are thoroughly
investigated. It is shown that due to the strong inter-subband scattering, the
spin procession and the spin dephasing rate of electrons in different subbands
are almost identical despite the large difference in the D'yakonov-Perel' (DP)
terms of different subbands. It is also shown that for quantum wells with small
well width at temperatures where only the lowest subband is occupied, the spin
dephasing time increases with the temperature as well as the applied in-plane
electric field until the contribution from the second subband is no longer
negligible. For wide quantum wells the spin dephasing time tends to decrease
with the temperature and the electric field.Comment: 6 pages, 4 figures in eps forma
Spin orientation of a two-dimensional electron gas by a high-frequency electric field
Coupling of spin states and space motion of conduction electrons due to
spin-orbit interaction opens up possibilities for manipulation of the electron
spins by electrical means. It is shown here that spin orientation of a
two-dimensional electron gas can be achieved by excitation of the carriers with
a linearly polarized high-frequency electric field. In (001)-grown quantum well
structures excitation with in-plane ac electric field induces orientation of
the electron spins along the quantum well normal, with the spin sign and the
magnitude depending on the field polarization.Comment: 5 pages, 1 figur
Frequency dependence of induced spin polarization and spin current in quantum wells
Dynamic response of two-dimensional electron systems with spin-orbit
interaction is studied theoretically on the basis of quantum kinetic equation,
taking into account elastic scattering of electrons. The spin polarization and
spin current induced by the applied electric field are calculated for the whole
class of electron systems described by p-linear spin-orbit Hamiltonians. The
absence of nonequilibrium intrinsic static spin currents is confirmed for these
systems with arbitrary (nonparabolic) electron energy spectrum. Relations
between the spin polarization, spin current, and electric current are
established. The general results are applied to the quantum wells grown in
[001] and [110] crystallographic directions, with both Rashba and Dresselhaus
types of spin-orbit coupling. It is shown that the existence of the fixed
(momentum-independent) precession axes in [001]-grown wells with equal Rashba
and Dresselhaus spin velocities or in symmetric [110]-grown wells leads to
vanishing spin polarizability at arbitrary frequency of the applied electric
field. This property is explained by the absence of Dyakonov-Perel-Kachorovskii
spin relaxation for the spins polarized along these precession axes. As a
result, a considerable frequency dispersion of spin polarization at very low
frequency in the vicinity of the fixed precession axes is predicted. Possible
effects of extrinsic spin-orbit coupling on the obtained results are discussed.Comment: 14 pages, 6 figures; published with minor corrections in Phys. Rev.
Spin-density induced by electromagnetic wave in two-dimensional electron gas with both Rashba and Dresselhaus spin-orbit couplings
We consider the magnetic response of a two-dimensional electron gas (2DEG)
with both Rashba and Dresselhaus spin-orbit coupling to a microwave excitation.
We generalize the results of [A. Shnirman and I. Martin, Europhys. Lett. 78,
27001 (2007).], where pure Rashba coupling was studied. We observe that the
microwave with the in-plane electric field and the out-of-plane magnetic field
creates an out-of-plane spin polarization. The effect is more prominent in
clean systems with resolved spin-orbit-split subbands. Considered as response
to the microwave magnetic field, the spin-orbit contribution to the
magnetization far exceeds the usual Zeeman contribution in the clean limit. The
effect vanishes when the Rashba and the Dresselhaus couplings have equal
strength.Comment: 4 pages, 2 figure
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