1,915 research outputs found
Zero- and one-dimensional magnetic traps for quasi-particles
We investigate the possibility of trapping quasi-particles possessing spin
degree of freedom in hybrid structures. The hybrid system we are considering
here is composed of a semi-magnetic quantum well placed a few nanometers below
a ferromagnetic micromagnet. We are interested in two different micromagnet
shapes: cylindrical (micro-disk) and rectangular geometry. We show that in the
case of a micro-disk, the spin object is localized in all three directions and
therefore zero-dimensional states are created, and in the case of an elongated
rectangular micromagnet, the quasi-particles can move freely in one direction,
hence one-dimensional states are formed. After calculating profiles of the
magnetic field produced by the micromagnets, we analyze in detail the possible
light absorption spectrum for different micromagnet thicknesses, and different
distances between the micromagnet and the semimagnetic quantum well. We find
that the discrete spectrum of the localized states can be detected via
spatially-resolved low temperature optical measurement.Comment: 15 pages, 9 figure
Spin-current modulation and square-wave transmission through periodically stubbed electron waveguides
Ballistic spin transport through waveguides, with symmetric or asymmetric
double stubs attached to them periodically, is studied systematically in the
presence of a weak spin-orbit coupling that makes the electrons precess. By an
appropriate choice of the waveguide length and of the stub parameters injected
spin-polarized electrons can be blocked completely and the transmission shows a
periodic and nearly square-type behavior, with values 1 and 0, with wide gaps
when only one mode is allowed to propagate in the waveguide. A similar behavior
is possible for a certain range of the stub parameters even when two-modes can
propagate in the waveguide and the conductance is doubled. Such a structure is
a good candidate for establishing a realistic spin transistor. A further
modulation of the spin current can be achieved by inserting defects in a
finite-number stub superlattice. Finite-temperature effects on the spin
conductance are also considered.Comment: 19 pages, 8 figure
A proposal for the measurement of Rashba and Dresselhaus spin-orbit interaction strengths in a single sample
We establish an exact analytical treatment for the determination of the
strengths of the Rashba and Dresselhaus spin-orbit interactions in a single
sample by measuring persistent spin current. A hidden symmetry is exploited in
the Hamiltonian to show that the spin current vanishes when the strength of the
Dresselhaus interaction becomes equal to the strength of the Rashba term. The
results are sustained even in the presence of disorder and thus an experiment
in this regard will be challenging.Comment: 5 pages, 5 figure
Spin Polarization at Semiconductor Point Contacts in Absence of Magnetic Field
Semiconductor point contacts can be a useful tool for producing
spin-polarized currents in the presence of spin-orbit (SO) interaction. Neither
magnetic fields nor magnetic materials are required. By numerical studies, we
show that (i) the conductance is quantized in units of 2e^2/h unless the SO
interaction is too strong, (ii) the current is spin-polarized in the transverse
direction, and (iii) a spin polarization of more than 50% can be realized with
experimentally accessible values of the SO interaction strength. The
spin-polarization ratio is determined by the adiabaticity of the transition
between subbands of different spins during the transport through the point
contacts.Comment: 4 pages, 4 figures; minor changes, published in J. Phys. Soc. Jp
Spin Accumulation in Quantum Wires with Strong Rashba Spin-Orbit Coupling
We present analytical and numerical results for the effect of Rashba
spin-orbit coupling on band structure, transport, and interaction effects in
quantum wires when the spin precession length is comparable to the wire width.
In contrast to the weak-coupling case, no common spin-quantization axis can be
defined for eigenstates within a single-electron band. The situation with only
the lowest spin-split subbands occupied is particularly interesting because
electrons close to Fermi points of the same chirality can have approximately
parallel spins. We discuss consequences for spin-dependent transport and
effective Tomonaga-Luttinger descriptions of interactions in the quantum wire.Comment: 4 pages, 4 figures, expanded discussion of spin accumulatio
Magnetization of a two-dimensional electron gas with a second filled subband
We have measured the magnetization of a dual-subband two-dimensional electron
gas, confined in a GaAs/AlGaAs heterojunction. In contrast to two-dimensional
electron gases with a single subband, we observe non-1/B-periodic, triangularly
shaped oscillations of the magnetization with an amplitude significantly less
than per electron. All three effects are explained by a
field dependent self-consistent model, demonstrating the shape of the
magnetization is dominated by oscillations in the confining potential.
Additionally, at 1 K, we observe small oscillations at magnetic fields where
Landau-levels of the two different subbands cross.Comment: 4 pages, 4 figure
Quantum gates with topological phases
We investigate two models for performing topological quantum gates with the
Aharonov-Bohm (AB) and Aharonov-Casher (AC) effects. Topological one- and
two-qubit Abelian phases can be enacted with the AB effect using charge qubits,
whereas the AC effect can be used to perform all single-qubit gates (Abelian
and non-Abelian) for spin qubits. Possible experimental setups suitable for a
solid state implementation are briefly discussed.Comment: 2 figures, RevTex
Mesoscopic Stern-Gerlach device to polarize spin currents
Spin preparation and spin detection are fundamental problems in spintronics
and in several solid state proposals for quantum information processing. Here
we propose the mesoscopic equivalent of an optical polarizing beam splitter
(PBS). This interferometric device uses non-dispersive phases (Aharonov-Bohm
and Rashba) in order to separate spin up and spin down carriers into distinct
outputs and thus it is analogous to a Stern-Gerlach apparatus. It can be used
both as a spin preparation device and as a spin measuring device by converting
spin into charge (orbital) degrees of freedom. An important feature of the
proposed spin polarizer is that no ferromagnetic contacts are used.Comment: Updated to the published versio
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