826 research outputs found
Spin injection and electric field effect in degenerate semiconductors
We analyze spin-transport in semiconductors in the regime characterized by
(intermediate to degenerate), where is the Fermi
temperature. Such a regime is of great importance since it includes the lightly
doped semiconductor structures used in most experiments; we demonstrate that,
at the same time, it corresponds to the regime in which carrier-carrier
interactions assume a relevant role. Starting from a general formulation of the
drift-diffusion equations, which includes many-body correlation effects, we
perform detailed calculations of the spin injection characteristics of various
heterostructures, and analyze the combined effects of carrier density
variation, applied electric field and Coulomb interaction. We show the
existence of a degenerate regime, peculiar to semiconductors, which strongly
differs, as spin-transport is concerned, from the degenerate regime of metals.Comment: Version accepted for publication in Phys. Rev.
Spin Precession and Oscillations in Mesoscopic Systems
We compare and contrast magneto-transport oscillations in the fully quantum
(single-electron coherent) and classical limits for a simple but illustrative
model. In particular, we study the induced magnetization and spin current in a
two-terminal double-barrier structure with an applied Zeeman field between the
barriers and spin disequilibrium in the contacts. Classically, the spin current
shows strong tunneling resonances due to spin precession in the region between
the two barriers. However, these oscillations are distinguishable from those in
the fully coherent case, for which a proper treatment of the electron phase is
required. We explain the differences in terms of the presence or absence of
coherent multiple wave reflections.Comment: 9 pages, 5 figure
Electric-field dependent spin diffusion and spin injection into semiconductors
We derive a drift-diffusion equation for spin polarization in semiconductors
by consistently taking into account electric-field effects and nondegenerate
electron statistics. We identify a high-field diffusive regime which has no
analogue in metals. In this regime there are two distinct spin diffusion
lengths. Furthermore, spin injection from a ferromagnetic metal into a
semiconductor is enhanced by several orders of magnitude and spins can be
transported over distances much greater than the low-field spin diffusion
length.Comment: 5 pages, 3 eps figure
Relativistic quantum model of confinement and the current quark masses
We consider a relativistic quantum model of confined massive spinning quarks
and antiquarks which describes leading Regge trajectories of mesons. The quarks
are described by the Dirac equations and the gluon contribution is approximated
by the Nambu-Goto straight-line string. The string tension and the current
quark masses are the main parameters of the model. Additional parameters are
phenomenological constants which approximate nonstring short-range
contributions. Comparison of the measured meson masses with the model
predictions allows one to determine the current quark masses (in MeV) to be
. The chiral
model[23] makes it possible to estimate from here the - and -quark masses
to be ~ Mev and Mev.Comment: 15 pages, LATEX, 2 tables. (submitted to Phys.Rev.D
Spin relaxation in the impurity band of a semiconductor in the external magnetic field
Spin relaxation in the impurity band of a 2D semiconductor with spin-split
spectrum in the external magnetic field is considered. Several mechanisms of
spin relaxation are shown to be relevant. The first one is attributed to
phonon-assisted transitions between Zeeman sublevels of the ground state of an
isolated impurity, while other mechanisms can be described in terms of spin
precession in a random magnetic field during the electron motion over the
impurity band. In the later case there are two contributions to the spin
relaxation: the one given by optimal impurity configurations with the
hop-waiting time inversely proportional to the external magnetic field and
another one related to the electron motion on a large scale. The average spin
relaxation rate is calculated
Dynamic Kerr Effect and Spectral Weight Transfer in the Manganites
We perform pump-probe Kerr spectroscopy in the colossally magnetoresistive
manganite Pr0.67Ca0.33MnO3. Kerr effects uncover surface magnetic dynamics
undetected by established methods based on reflectivity and optical spectral
weight transfer. Our findings indicate the connection between spin and charge
dynamics in the manganites may be weaker than previously thought. Additionally,
important differences between this system and conventional ferromagnetic metals
manifest as long-lived, magneto-optical coupling transients, which may be
generic to all manganites.Comment: 12 text pages, 4 figure
Fabrication and Characterization of Modulation-Doped ZnSe/(Zn,Cd)Se (110) Quantum Wells: A New System for Spin Coherence Studies
We describe the growth of modulation-doped ZnSe/(Zn,Cd)Se quantum wells on
(110) GaAs substrates. Unlike the well-known protocol for the epitaxy of
ZnSe-based quantum structures on (001) GaAs, we find that the fabrication of
quantum well structures on (110) GaAs requires significantly different growth
conditions and sample architecture. We use magnetotransport measurements to
confirm the formation of a two-dimensional electron gas in these samples, and
then measure transverse electron spin relaxation times using time-resolved
Faraday rotation. In contrast to expectations based upon known spin relaxation
mechanisms, we find surprisingly little difference between the spin lifetimes
in these (110)-oriented samples in comparison with (100)-oriented control
samples.Comment: To appear in Journal of Superconductivity (Proceedings of 3rd
Conference on Physics and Applications of Spin-dependent Phenomena in
Semiconductors
Coulomb interaction effects in spin-polarized transport
We study the effect of the electron-electron interaction on the transport of
spin polarized currents in metals and doped semiconductors in the diffusive
regime. In addition to well-known screening effects, we identify two additional
effects, which depend on many-body correlations and exchange and reduce the
spin diffusion constant. The first is the "spin Coulomb drag" - an intrinsic
friction mechanism which operates whenever the average velocities of up-spin
and down-spin electrons differ. The second arises from the decrease in the
longitudinal spin stiffness of an interacting electron gas relative to a
noninteracting one. Both effects are studied in detail for both degenerate and
non-degenerate carriers in metals and semiconductors, and various limiting
cases are worked out analytically. The behavior of the spin diffusion constant
at and below a ferromagnetic transition temperature is also discussed.Comment: 9 figure
Spin diffusion and injection in semiconductor structures: Electric field effects
In semiconductor spintronic devices, the semiconductor is usually lightly
doped and nondegenerate, and moderate electric fields can dominate the carrier
motion. We recently derived a drift-diffusion equation for spin polarization in
the semiconductors by consistently taking into account electric-field effects
and nondegenerate electron statistics and identified a high-field diffusive
regime which has no analogue in metals. Here spin injection from a ferromagnet
(FM) into a nonmagnetic semiconductor (NS) is extensively studied by applying
this spin drift-diffusion equation to several typical injection structures such
as FM/NS, FM/NS/FM, and FM/NS/NS structures. We find that in the high-field
regime spin injection from a ferromagnet into a semiconductor is enhanced by
several orders of magnitude. For injection structures with interfacial
barriers, the electric field further enhances spin injection considerably. In
FM/NS/FM structures high electric fields destroy the symmetry between the two
magnets at low fields, where both magnets are equally important for spin
injection, and spin injection becomes locally determined by the magnet from
which carriers flow into the semiconductor. The field-induced spin injection
enhancement should also be insensitive to the presence of a highly doped
nonmagnetic semiconductor (NS) at the FM interface, thus FM/NS/NS
structures should also manifest efficient spin injection at high fields.
Furthermore, high fields substantially reduce the magnetoresistance observable
in a recent experiment on spin injection from magnetic semiconductors
Room temperature and low-field resonant enhancement of spin Seebeck effect in partially compensated magnets
Resonant enhancement of spin Seebeck effect (SSE) due to phonons was recently
discovered in Y3Fe5O12 (YIG). This effect is explained by hybridization between
the magnon and phonon dispersions. However, this effect was observed at low
temperatures and high magnetic fields, limiting the scope for applications.
Here we report observation of phonon-resonant enhancement of SSE at room
temperature and low magnetic field. We observed in Lu2BiFe4GaO12 and
enhancement 700 % greater than that in a YIG film and at very low magnetic
fields around 10-1 T, almost one order of magnitude lower than that of YIG. The
result can be explained by the change in the magnon dispersion induced by
magnetic compensation due to the presence of non-magnetic ion substitutions.
Our study provides a way to tune the magnon response in a crystal by chemical
doping with potential applications for spintronic devices.Comment: 17 pages, 4 figure
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