1,395 research outputs found
Spin extraction theory and its relevance to spintronics
Extraction of electrons from a semiconductor to a ferromagnet as well as the
case of injection in the reverse direction may be formulated as a scattering
theory. However, the presence of bound states at the interface arising out of
doping on the semiconductor side must be taken into account in the scattering
theory. Inclusion of the interface states yields an explanation of a recent
result of spin imaging measurement which contradicts the current understanding
of spin extraction. The importance of an extraction theory to spintronics is
illustrated by an application to a spin switch.Comment: 4 two column pages, 3 figures, major revisions to improve the
presentation. in addition, the new version includes an electrically
controlled spin switc
Electric readout of magnetization dynamics in a ferromagnet-semiconductor system
We apply an analysis of time-dependent spin-polarized current in a
semiconductor channel at room temperature to establish how the magnetization
configuration and dynamics of three ferromagnetic terminals, two of them biased
and third connected to a capacitor, affect the currents and voltages. In a
steady state, the voltage on the capacitor is related to spin accumulation in
the channel. When the magnetization of one of the terminals is rotated, a
transient current is triggered. This effect can be used for electrical
detection of magnetization reversal dynamics of an electrode or for dynamical
readout of the alignment of two magnetic contacts.Comment: Revised version, 8 pages, 3 figure
Quantum Dynamics of a Nanomagnet driven by Spin-Polarized Current
A quantum theory of magnetization dynamics of a nanomagnet as a sequence of
scatterings of each electron spin with the macrospin state of the magnetization
results in each encounter a probability distribution of the magnetization
recoil state associated with each outgoing state of the electron. The quantum
trajectory of the magnetization contains the average motion tending in the
large spin limit to the semi-classical results of spin transfer torque and the
fluctuations giving rise to a quantum magnetization noise and an additional
noise traceable to the current noise.Comment: 4 pages, 4 figure
Lateral diffusive spin transport in layered structures
A one dimensional theory of lateral spin-polarized transport is derived from
the two dimensional flow in the vertical cross section of a stack of
ferromagnetic and paramagnetic layers. This takes into account the influence of
the lead on the lateral current underneath, in contrast to the conventional 1D
modeling by the collinear configuration of lead/channel/lead. Our theory is
convenient and appropriate for the current in plane configuration of an
all-metallic spintronics structure as well as for the planar structure of a
semiconductor with ferromagnetic contacts. For both systems we predict the
optimal contact width for maximal magnetoresistance and propose an electrical
measurement of the spin diffusion length for a wide range of materials.Comment: 4 pages, 3 figure
Spintronics for electrical measurement of light polarization
The helicity of a circularly polarized light beam may be determined by the
spin direction of photo-excited electrons in a III-V semiconductor. We present
a theoretical demonstration how the direction of the ensuing electron spin
polarization may be determined by electrical means of two
ferromagnet/semiconductor Schottky barriers. The proposed scheme allows for
time-resolved detection of spin accumulation in small structures and may have a
device application.Comment: Revised version, 8 two-column pages, 5 figures; Added: a
comprehensive time dependent analysis, figures 3b-3c & 5, equations 6 & 13-16
and 3 references. submitted to Phys. Rev.
Quasiparticle Band Structure and Density Functional Theory: Single-Particle Excitations and Band Gaps in Lattice Models
We compare the quasiparticle band structure for a model insulator obtained
from the fluctuation exchange approximation (FEA) with the eigenvalues of the
corresponding density functional theory (DFT) and local density approximation
(LDA). The discontinuity in the exchange-correlation potential for this model
is small and the FEA and DFT band structures are in good agreement. In contrast
to conventional wisdom, the LDA for this model overestimates the size of the
band gap. We argue that this is a consequence of an FEA self-energy that is
strongly frequency dependent, but essentially local.Comment: 8 pages, and 5 figure
Nanodot-Cavity Electrodynamics and Photon Entanglement
Quantum electrodynamics of excitons in a cavity is shown to be relevant to
quantum operations. We present a theory of an integrable solid-state quantum
controlled-phase gate for generating entanglement of two photons using a
coupled nanodot-microcavity-fiber structure. A conditional phase shift of
is calculated to be the consequence of the giant optical
nonlinearity keyed by the excitons in the cavities. Structural design and
active control, such as electromagnetic induced transparency and pulse shaping,
optimize the quantum efficiency of the gate operation.Comment: 4 pages 3 figure
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