110 research outputs found
2D superconductivity with strong spin-orbit interaction
We consider superconductivity confined at a two-dimensional interface with a
strong surface spin-orbit (Rashba) interaction. Some peculiar properties of
this system are investigated. In particular, we show that an in-plane Zeeman
field can induce a supercurrent flow.Comment: latex, 1 figure in ep
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
Spin Transfer from a Ferromagnet into a Semiconductor through an Oxide barrier
We present results on the magnetoresistance of the system Ni/Al203/n-doped
Si/Al2O3/Ni in fabricated nanostructures. The results at temperature of 14K
reveal a 75% magnetoresistance that decreases in value up to approximately 30K
where the effect disappears. We observe minimum resistance in the antiparallel
configurations of the source and drain of Ni. As a possibility, it seems to
indicate the existence of a magnetic state at the Si/oxide interface. The
average spin diffusion length obtained is of 650 nm approximately. Results are
compared to the window of resistances that seems to exist between the tunnel
barrier resistance and two threshold resistances but the spin transfer seems to
work in the range and outside the two thresholds
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
Theory of combined exciton-cyclotron resonance in a two-dimensional electron gas: The strong magnetic field regime
I develop a theory of combined exciton-cyclotron resonance (ExCR) in a
low-density two-dimensional electron gas in high magnetic fields. In the
presence of excess electrons an incident photon creates an exciton and
simultaneously excites one electron to higher-lying Landau levels. I derive
exact ExCR selection rules that follow from the existing dynamical symmetries,
magnetic translations and rotations about the magnetic field axis. The nature
of the final states in the ExCR is elucidated. The relation between ExCR and
shake-up processes is discussed. The double-peak ExCR structure for transitions
to the first electron Landau level is predicted.Comment: 5 pages, 3 figures, replaced with the published versio
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
Filtering spin with tunnel-coupled electron wave guides
We show how momentum-resolved tunneling between parallel electron wave guides
can be used to observe and exploit lifting of spin degeneracy due to Rashba
spin-orbit coupling. A device is proposed that achieves spin filtering without
using ferromagnets or the Zeeman effect.Comment: 4 pages, 4 figures, RevTex
Dissipation effects in spin-Hall transport of electrons and holes
We investigate the spin-Hall effect of both electrons and holes in
semiconductors using the Kubo formula in the correct zero-frequency limit
taking into account the finite momentum relaxation time of carriers in real
semiconductors. This approach allows to analyze the range of validity of recent
theoretical findings. In particular, the spin-Hall conductivity vanishes for
vanishing spin-orbit coupling if the correct zero-frequency limit is performed.Comment: 5 pages, no figures, version to appear in Phys. Rev.
Spin Injection in a Ballistic Two-Dimensional Electron Gas
We explore electrically injected, spin polarized transport in a ballistic
two-dimensional electron gas. We augment the Buettiker-Landauer picture with a
simple, but realistic model for spin-selective contacts to describe multimode
reservoir-to-reservoir transport of ballistic spin 1/2 particles. Clear and
unambiguous signatures of spin transport are established in this regime, for
the simplest measurement configuration that demonstrates them directly. These
new effects originate from spin precession of ballistic carriers; they exhibit
strong dependence upon device geometry and vanish in the diffusive limit. Our
results have important implications for prospective ``spin transistor''
devices.Comment: Submitted to Phys. Rev. Let
Spin transport of electrons through quantum wires with spatially-modulated strength of the Rashba spin-orbit interaction
We study ballistic transport of spin-polarized electrons through quantum
wires in which the strength of the Rashba spin-orbit interaction (SOI) is
spatially modulated. Subband mixing, due to SOI, between the two lowest
subbands is taken into account. Simplified approximate expressions for the
transmission are obtained for electron energies close to the bottom of the
first subband and near the value for which anticrossing of the two lowest
subbands occurs. In structures with periodically varied SOI strength, {\it
square-wave} modulation on the spin transmission is found when only one subband
is occupied and its possible application to the spin transistor is discussed.
When two subbands are occupied the transmission is strongly affected by the
existence of SOI interfaces as well as by the subband mixing
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