432 research outputs found
The evolution of Bernstein modes in quantum wires with increasing deviation from parabolic confinement
We investigate the evolution of the interaction of the magnetoplasmon
resonance with the harmonics of the cyclotron resonance as the confinement of
an electron gas in a quantum wire increasingly deviates from the parabolic
case. The occurrence of the Bernstein modes is observed in a time-dependent
Hartree model of a two-dimensional electron gas in a single quantum wire.Comment: 9 pages, 4 figures, uses IOP macros, to appear in the Journal of
Physics: Condensed Matte
Current and Spin-Torque in Double Tunnel Barrier Ferromagnet - Superconductor - Ferromagnet Systems
We calculate the current and the spin-torque in small symmetric double tunnel
barrier ferromagnet - superconductor - ferromagnet (F-S-F) systems.
Spin-accumulation on the superconductor governs the transport properties when
the spin-flip relaxation time is longer than the transport dwell time. In the
elastic transport regime, it is demonstrated that the relative change in the
current (spin-torque) for F-S-F systems equals the relative change in the
current (spin-torque) for F-N-F systems upon changing the relative
magnetization direction of the two ferromagnets. This differs from the results
in the inelastic transport regime where spin-accumulation suppresses the
superconducting gap and dramatically changes the magnetoresistance [S.
Takahashi, H. Imamura, and S. Maekawa, Phys. Rev. Lett. 82, 3911 (1999)]. The
experimental relevance of the elastic and inelastic transport regimes,
respectively, as well as the reasons for the change in the transport properties
are discussed.Comment: 7 page
Spin Injection in Quantum Wells with Spatially Dependent Rashba Interaction
We consider Rashba spin-orbit effects on spin transport driven by an electric
field in semiconductor quantum wells. We derive spin diffusion equations that
are valid when the mean free path and the Rashba spin-orbit interaction vary on
length scales larger than the mean free path in the weak spin-orbit coupling
limit. From these general diffusion equations, we derive boundary conditions
between regions of different spin-orbit couplings. We show that spin injection
is feasible when the electric field is perpendicular to the boundary between
two regions. When the electric field is parallel to the boundary, spin
injection only occurs when the mean free path changes within the boundary, in
agreement with the recent work by Tserkovnyak et al. [cond-mat/0610190].Comment: 7 pages, 1 figur
The effects of compressible and incompressible states on the FIR-absorption of quantum wires and dots in a magnetic field
We investigate the effects of compressible and incompressible states on the
FIR-absorption of quantum wires and dots in a homogeneous perpendicular
magnetic field. The electron-electron interaction is treated in the Hartree
approximation at a finite low temperature. The calculated dispersion of the
collective excitations reproduces several experimental results.Comment: To be published by Physica Scripta in the proceedings of the 17NSM. 6
pages in LaTeX + 6 postscript figure
Current-driven skyrmion Depinning in Magnetic Granular Films
We consider current-driven motion of magnetic skyrmions in granular magnetic
films. The study uses micromagnetic modeling and phenomenological analysis
based on the Thiele formalism. Remarkably, disorder enhances the effective
skyrmion Hall effect that depends on the magnitude of the driving force
(current density and non-adiabaticity parameter). The origin is sliding motion
of the skyrmion along the grain boundaries, followed by pinning and depinning
at the grain junctions. A side-jump can occur during this depinning process. In
addition, the critical current that triggers the skyrmion motion depends on the
relative size of the crystallites with respect to the skyrmion size. Finally,
when the skyrmion trajectory is confined along an edge by the non-adiabatic
Magnus force, the critical current density can be significantly reduced. Our
results imply that narrow nanowires have higher skyrmion mobilities.Comment: 8 pages, 7 figure
Bulk and edge spin transport in topological magnon insulators
We investigate the spin transport properties of a topological magnon
insulator, a magnetic insulator characterized by topologically nontrivial bulk
magnon bands and protected magnon edge modes located in the bulk band gaps.
Employing the Landau-Lifshitz-Gilbert phenomenology, we calculate the spin
current driven through a normal metaltopological magnon insulatornormal
metal heterostructure by a spin accumulation imbalance between the metals, with
and without random lattice defects. We show that bulk and edge transport are
characterized by different length scales. This results in a characteristic
system size where the magnon transport crosses over from being bulk-dominated
for small systems to edge-dominated for larger systems. These findings are
generic and relevant for topological transport in systems of nonconserved
bosons.Comment: 5 pages, 5 figures, 3 pages Supplemental Material with 2 additional
figure
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