239,908 research outputs found
Magnetic forces and localized resonances in electron transfer through quantum rings
We study the current flow through semiconductor quantum rings. In high
magnetic field the current is usually injected to the arm of the ring preferred
by classical magnetic forces. However, for narrow magnetic field intervals that
appear periodically on the magnetic field scale the current is injected to the
other arm of the ring. We indicate that the appearance of the anomalous --
non-classical -- current circulation results from Fano interference involving
localized resonant states. The identification of the Fano interference is based
on the comparison of the solution of the scattering problem with the results of
the stabilization method. The latter employs the bound-state type calculations
and allows to extract both the energy of metastable states localized within the
ring and the width of resonances by analysis of the energy spectrum of a finite
size system in function of its length. The Fano resonances involving states of
anomalous current circulation become extremely narrow on both magnetic field
and energy scales. This is consistent with the orientation of the Lorentz force
that tends to keep the electron within the ring and thus increases the lifetime
of the electron localization within the ring. Absence of periodic Fano
resonances in electron transfer probability through a quantum ring containing
an elastic scatterer is also explained.Comment: This paper explains the origins of anomalous (non-classical) current
circulation reported in http://arxiv.org/abs/1004.219
A statistical study of the global structure of the ring current
[1] In this paper we derive the average configuration of the ring current as a function of the state of the magnetosphere as indicated by the Dst index. We sort magnetic field data from the Combined Release and Radiation Effects Satellite (CRRES) by spatial location and by the Dst index in order to produce magnetic field maps. From these maps we calculate local current systems by taking the curl of the magnetic field. We find both the westward (outer) and the eastward (inner) components of the ring current. We find that the ring current intensity varies linearly with Dst as expected and that the ring current is asymmetric for all Dst values. The azimuthal peak of the ring current is located in the afternoon sector for quiet conditions and near midnight for disturbed conditions. The ring current also moves closer to the Earth during disturbed conditions. We attempt to recreate the Dst index by integrating the magnetic perturbations caused by the ring current. We find that we need to multiply our computed disturbance by a factor of 1.88 ± 0.27 and add an offset of 3.84 ± 4.33 nT in order to get optimal agreement with Dst. When taking into account a tail current contribution of roughly 25%, this agrees well with our expectation of a factor of 1.3 to 1.5 based on a partially conducting Earth. The offset that we have to add does not agree well with an expected offset of approximately 20 nT based on solar wind pressure
Persistent spin current and entanglement in the anisotropic spin ring i
We investigate the ground state persistent spin current and the pair
entanglement in one-dimensional antiferromagnetic anisotropic Heisenberg ring
with twisted boundary conditions. Solving Bethe ansatz equations numerically,
we calculate the dependence of the ground state energy on the total magnetic
flux through the ring, and the resulting persistent current. Motivated by
recent development of quantum entanglement theory, we study the properties of
the ground state concurrence under the influence of the flux through the
anisotropic Heisenberg ring. We also include an external magnetic field and
discuss the properties of the persistent current and the concurrence in the
presence of the magnetic field.Comment: 5 pages, 8 figure
A review of the Jovian magnetosphere based upon Pioneer 10 and 11
Data derived from the plasma, magnetic field, and energetic particle experiments on the December, 1973 and December, 1974 Jupiter encounters are reviewed. A bow shock was discovered on the solar side of the planet, as predicted. However, a smaller magnetic field and larger fluxes of energetic electrons were found than anticipated. A ring current and current sheet in the Jovian plasmasphere are inferred from magnetic field measurements
Aharonov-Casher oscillations of spin current through a multichannel mesoscopic ring
The Aharonov-Casher (AC) oscillations of spin current through a 2D ballistic
ring in the presence of Rashba spin-orbit interaction and external magnetic
field has been calculated using the semiclassical path integral method. For
classically chaotic trajectories the Fokker-Planck equation determining
dynamics of the particle spin polarization has been derived. On the basis of
this equation an analytic expression for the spin conductance has been obtained
taking into account a finite width of the ring arms carrying large number of
conducting channels. It was shown that the finite width results in a broadening
and damping of spin current AC oscillations. We found that an external magnetic
field leads to appearance of new nondiagonal components of the spin
conductance, allowing thus by applying a rather weak magnetic field to change a
direction of the transmitted spin current polarization.Comment: 16 pages, 6 figure
CURRENT MAGNIFICATION AND CIRCULATING CURRENTS IN MESOSCOPIC RINGS
We show that several novel effects related to persistent currents can arise
in open systems, which have no analogue in closed or isolated systems. We have
considered a system of a metallic ring coupled to two electron reservoirs. We
show that in the presence of a transport current, persistent currents can flow
in a ring even in the absence of magnetic field. This is related to the current
magnification effect in the ring. In the presence of magnetic field we show
that the amplitude of persistent currents is sensitive to the direction of
current flow from one reservoir to another. Finally we briefly discuss the
persistent currents arising due to two nonclassical effects namely,
Aharonov-Bohm effect and quantum tunneling.Comment: On the basis of talk given by A. M. Jayannavar at "International
Workshop on Novel Physics in Low Dimensional Systems" in Madras(India). Four
figures available on reques
Simulations of inner magnetosphere dynamics with an expanded RAM-SCB model and comparisons with Van Allen Probes observations
Abstract Simulations from our newly expanded ring current-atmosphere interactions model with self-consistent magnetic field (RAM-SCB), now valid out to 9 R E, are compared for the first time with Van Allen Probes observations. The expanded model reproduces the storm time ring current buildup due to the increased convection and inflow of plasma from the magnetotail. It matches Magnetic Electron Ion Spectrometer (MagEIS) observations of the trapped high-energy (\u3e50 keV) ion flux; however, it underestimates the low-energy (\u3c10 keV) Helium, Oxygen, Proton, and Electron (HOPE) observations. The dispersed injections of ring current ions observed with the Energetic particle, Composition, and Thermal plasma (ECT) suite at high (\u3e20 keV) energy are better reproduced using a high-resolution convection model. In agreement with Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations, RAM-SCB indicates that the large-scale magnetic field is depressed as close as ∼4.5 RE during even a moderate storm. Regions of electromagnetic ion cyclotron instability are predicted on the duskside from ∼6 to ∼9 RE, indicating that previous studies confined to geosynchronous orbit may have underestimated their scattering effect on the energetic particles. Key Points Expanded RAM-SCB model reproduces well high-energy (\u3e50 keV) MagEIS observations The magnetic field is depressed as close as ∼4.5 RE during even a moderate storm EMIC wave growth extends on duskside from ∼6 to ∼9 RE during storm main phase
Currents and pseudomagnetic fields in strained graphene rings
We study the effects of strain on the electronic properties and persistent
current characteristics of a graphene ring using the Dirac representation. For
a slightly deformed graphene ring flake, one obtains sizable pseudomagnetic
(gauge) fields that may effectively reduce or enhance locally the applied
magnetic flux through the ring. Flux-induced persistent currents in a flat ring
have full rotational symmetry throughout the structure; in contrast, we show
that currents in the presence of a circularly symmetric deformation are
strongly inhomogeneous, due to the underlying symmetries of graphene. This
result illustrates the inherent competition between the `real' magnetic field
and the `pseudo' field arising from strains, and suggest an alternative way to
probe the strength and symmetries of pseudomagnetic fields on graphene systems
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