2,264 research outputs found
Magnon spin Hall magnetoresistance of a gapped quantum paramagnet
Motivated by recent experimental work, we consider spin transport between a
normal metal and a gapped quantum paramagnet. We model the latter as the
magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We
evaluate the spin current mediated by the interface exchange coupling between
the ferromagnet and the adjacent normal metal. For the strongly interacting
magnons that we consider, this spin current gives rise to a spin Hall
magnetoresistance that strongly depends on the magnitude of the magnetic field,
rather than its direction. This Letter may motivate electrical detection of the
phases of quantum magnets and the incorporation of such materials into
spintronic devices.Comment: 5 pages, 5 figure
Quasi-ballistic, nonequilibrium electron distribution in inhomogeneous semiconductor structures
We report on a study of quasi-ballistic transport in deep submicron,
inhomogeneous semiconductor structures, focusing on the analysis of signatures
found in the full nonequilibrium electron distribution. We perform
self-consistent numerical calculations of the Poisson-Boltzmann equations for a
model n(+)-n(-)-n(+) GaAs structure and realistic, energy-dependent scattering.
We show that, in general, the electron distribution displays significant,
temperature dependent broadening and pronounced structure in the high-velocity
tail of the distribution. The observed characteristics have a strong spatial
dependence, related to the energy-dependence of the scattering, and the large
inhomogeneous electric field variations in these systems. We show that in this
quasi-ballistic regime, the high-velocity tail structure is due to pure
ballistic transport, whereas the strong broadening is due to electron
scattering within the channel, and at the source(drain) interfaces.Comment: 4 pages, 2 figure
Landau level mixing by full spin-orbit interactions
We study a two-dimensional electron gas in a perpendicular magnetic field in
the presence of both Rashba and Dresselhaus spin-orbit interactions. Using a
Bogoliubov transformation we are able to write an approximate formula for the
Landau levels, thanks to the simpler form of the resulting Hamiltonian. The
exact numerical calculation of the energy levels, is also made simpler by our
formulation. The approximate formula and the exact numerical results show
excellent agreement for typical semiconductors, especially at high magnetic
fields. We also show how effective Zeeman coupling is modified by spin-orbit
interactions.Comment: 5 pages, 5 figure
Lateral spin-orbit interaction and spin polarization in quantum point contacts
We study ballistic transport through semiconductor quantum point contact
systems under different confinement geometries and applied fields. In
particular, we investigate how the {\em lateral} spin-orbit coupling,
introduced by asymmetric lateral confinement potentials, affects the spin
polarization of the current. We find that even in the absence of external
magnetic fields, a variable {\em non-zero spin polarization} can be obtained by
controlling the asymmetric shape of the confinement potential. These results
suggest a new approach to produce spin polarized electron sources and we study
the dependence of this phenomenon on structural parameters and applied magnetic
fields. This asymmetry-induced polarization provides also a plausible
explanation of our recent observations of a 0.5 conductance plateau (in units
of ) in quantum point contacts made on InAs quantum-well structures.
Although our estimates of the required spin-orbit interaction strength in these
systems do not support this explanation, they likely play a role in the effects
enhanced by electron-electron interactions.Comment: Summited to PRB (2009
Nonlocal Spin Transport as a Probe of Viscous Magnon Fluids
Magnons in ferromagnets behave as a viscous fluid over a length scale, the
momentum-relaxation length, below which momentum-conserving scattering
processes dominate. We show theoretically that in this hydrodynamic regime
viscous effects lead to a sign change in the magnon chemical potential, which
can be detected as a sign change in the nonlocal resistance measured in spin
transport experiments. This sign change is observable when the
injector-detector distance becomes comparable to the momentum-relaxation
length. Taking into account momentum- and spin-relaxation processes, we
consider the quasiconservation laws for momentum and spin in a magnon fluid.
The resulting equations are solved for nonlocal spin transport devices in which
spin is injected and detected via metallic leads. Because of the finite
viscosity we also find a backflow of magnons close to the injector lead. Our
work shows that nonlocal magnon spin transport devices are an attractive
platform to develop and study magnon-fluid dynamics
Optimal deployment of next-generation PON for high and ultra-high bandwidth demand scenarios in large urban areas
This paper proposes a techno-economic analysis of the optimal deployment of multiple PON networks with different technologies, including the newest next-generation standards, such as GPON, XGSPON, NG-PON2 and 50G-EPON, within a large urban area in Quito. On this zone, we simulated a population of around 20000 customers, distributed between two central offices. We assume that customers demand different bitrates considering present and future bitrate-demand scenarios. This analysis uses an algorithm called OTS (Optimal Topology Search) which employs a nested set of heuristics in order to find the optimal topology for the deployment of PON in large areas with many potential customers. Results obtained in this research describe an accurate projection of the optimal deployment cost and the most suitable PON technology for each bitrate demand scenario, taking into account not only the cost of the entire hardware, but leasing, labor-hours, pole-works and trenching/recapping-works
Magnetoexcitons in quantum-ring structures: a novel magnetic interference effect
A novel magnetic interference effect is proposed for a neutral, but
polarizable exciton in a quantum ring with a finite width. The magnetic
interference effect originates from the nonzero dipole moment in the exciton.
The ground state of exciton acquires a nonzero angular momentum with increasing
normal magnetic field. This leads to the suppression of the photoluminescence
in defined windows of the magnetic field.Comment: 6 pages, 2 figures, Proceed. EP2DS, 2001 (Physica E
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