85 research outputs found
Electrical Spin Injection in a Ferromagnetic / Tunnel Barrier/ Semiconductor Heterostructure
We demonstrate experimentally the electrical ballistic electron spin
injection from a ferromagnetic metal / tunnel barrier contact into a
semiconductor III-V heterostructure. We introduce the Oblique Hanle Effect
technique for reliable optical measurement of the degree of injected spin
polarization. In a CoFe / Al2O3 / GaAs / (Al,Ga)As heterostructure we observed
injected spin polarization in excess of 8 % at 80K.Comment: 5 pages, 4 figure
Effect of temperature variation on shift and broadening of exciton band in Cs₃Bi₂I₉ layered crystals
The exciton reflection spectra of Cs₃Bi₂I₉ layered crystals is investigated in the temperature region
4.2–300 K with light polarization E ⊥ c. It is estimated that the energy gap Eg equals
2.857 eV (T = 4.2 K) and the exciton binding energy Ry is 279 meV. A nontraditional temperature
shift of Eg(T) for the layered substances is found for the first time. It is learned that this shift is
described very well by the Varshni formula. A transition region in the temperature broadening of
the half-width H(T) of the exciton band with the increase of temperature is registered in the interval
between 150 and 220 K. It is shown that this region may be identified as the heterophase structure
region where ferroelastic and paraelastic phases coexist. A surge of H(T) at the point of the
ferroelastic phase transition (Tc = 220 K) is also observed
Spin-Polarized Electron Transport at Ferromagnet/Semiconductor Schottky Contacts
We theoretically investigate electron spin injection and spin-polarization
sensitive current detection at Schottky contacts between a ferromagnetic metal
and an n-type or p-type semiconductor. We use spin-dependent continuity
equations and transport equations at the drift-diffusion level of
approximation. Spin-polarized electron current and density in the semiconductor
are described for four scenarios corresponding to the injection or the
collection of spin polarized electrons at Schottky contacts to n-type or p-type
semiconductors. The transport properties of the interface are described by a
spin-dependent interface resistance, resulting from an interfacial tunneling
region. The spin-dependent interface resistance is crucial for achieving spin
injection or spin polarization sensitivity in these configurations. We find
that the depletion region resulting from Schottky barrier formation at a
metal/semiconductor interface is detrimental to both spin injection and spin
detection. However, the depletion region can be tailored using a doping density
profile to minimize these deleterious effects. For example, a heavily doped
region near the interface, such as a delta-doped layer, can be used to form a
sharp potential profile through which electrons tunnel to reduce the effective
Schottky energy barrier that determines the magnitude of the depletion region.
The model results indicate that efficient spin-injection and spin-polarization
detection can be achieved in properly designed structures and can serve as a
guide for the structure design.Comment: RevTex
Double detected spin-dependent quantum dot
We study the dynamics of a spin-dependent quantum dot system, where an
unsharp and a sharp detection scenario is introduced. The back-action of the
unsharp detection related to the magnetization, proposed in terms of the
continuous quantum measurement theory, is observed via the von Neumann
measurement (sharp detection) of the electric charge current. The behavior of
the average electron charge current is studied as a function of the unsharp
detection strength \gamma, and features of measurement back-action are
discussed. The achieved equations reproduce the quantum Zeno effect.
Considering magnetic leads, we demonstrate that the measurement process may
freeze the system in its initial state. We show that the continuous observation
may enhance the transition between spin states, in contradiction with rapidly
repeated projective observations, when it slows down. Experimental issue, such
as the accuracy of the electric current measurement, is analyzed.Comment: 20 pages, 7 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
Selective Spin Injection Controlled by Electrical way in Ferromagnet/Quantum Dot/Semiconductor system
Selective and large polarization of current injected into semiconductor (SC)
is predicted in Ferromagnet (FM)/Quantum Dot (QD)/SC system by varying the gate
voltage above the Kondo temperature. In addition, spin-dependent Kondo effect
is also revealed below Kondo temperature. It is found that Kondo resonances for
up spin state is suppressed with increasing of the polarization P of the FM
lead. While the down one is enhanced. The Kondo peak for up spin is disappear
at P=1
Monte Carlo Modeling of Spin FETs Controlled by Spin-Orbit Interaction
A method for Monte Carlo simulation of 2D spin-polarized electron transport
in III-V semiconductor heterojunction FETs is presented. In the simulation, the
dynamics of the electrons in coordinate and momentum space is treated
semiclassically. The density matrix description of the spin is incorporated in
the Monte Carlo method to account for the spin polarization dynamics. The
spin-orbit interaction in the spin FET leads to both coherent evolution and
dephasing of the electron spin polarization. Spin-independent scattering
mechanisms, including optical phonons, acoustic phonons and ionized impurities,
are implemented in the simulation. The electric field is determined
self-consistently from the charge distribution resulting from the electron
motion. Description of the Monte Carlo scheme is given and simulation results
are reported for temperatures in the range 77-300 K.Comment: 18 pages, 7 figure
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