9,462 research outputs found
The Scaling of the Anomalous Hall Effect in the Insulating Regime
We develop a theoretical approach to study the scaling of anomalous Hall
effect (AHE) in the insulating regime, which is observed to be
in experiments over a large
range of materials. This scaling is qualitatively different from the ones
observed in metals. Basing our theory on the phonon-assisted hopping mechanism
and percolation theory, we derive a general formula for the anomalous Hall
conductivity, and show that it scales with the longitudinal conductivity as
with predicted to be
, quantitatively in agreement with the experimental
observations. Our result provides a clearer understanding of the AHE in the
insulating regime and completes the scaling phase diagram of the AHE.Comment: 4 pages, 4 figures, plus the supplementary information. Minor
revisions made according to Referee report
Interaction between a fast rotating sunspot and ephemeral regions as the origin of the major solar event on 2006 December 13
The major solar event on 2006 December 13 is characterized by the
approximately simultaneous occurrence of a heap of hot ejecta, a great
two-ribbon flare and an extended Earth-directed coronal mass ejection. We
examine the magnetic field and sunspot evolution in active region NOAA AR
10930, the source region of the event, while it transited the solar disk centre
from Dec. 10 to Dec. 13. We find that the obvious changes in the active region
associated with the event are the development of magnetic shear, the appearance
of ephemeral regions and fast rotation of a smaller sunspot. Around the area of
the magnetic neutral line of the active region, interaction between the fast
rotating sunspot and the ephemeral regions triggers continual brightening and
finally the major flare. It is indicative that only after the sunspot rotates
up to 200 does the major event take place. The sunspot rotates at
least 240 about its centre, the largest sunspot rotation angle which
has been reported.Comment: 4 pages, 6 figures, ApJ Letters inpres
Diffusion-limited loop formation of semiflexible polymers: Kramers theory and the intertwined time scales of chain relaxation and closing
We show that Kramers rate theory gives a straightforward, accurate estimate
of the closing time of a semiflexible polymer that is valid in cases
of physical interest. The calculation also reveals how the time scales of chain
relaxation and closing are intertwined, illuminating an apparent conflict
between two ways of calculating in the flexible limit.Comment: Europhys. Lett., 2003 (in press). 8 pages, 3 figures. See also,
physics/0101087 for physicist's approach to and the importance of
semiflexible polymer looping, in DNA replicatio
Continuous Transition between Antiferromagnetic Insulator and Paramagnetic Metal in the Pyrochlore Iridate Eu2Ir2O7
Our single crystal study of the magneto-thermal and transport properties of
the pyrochlore iridate Eu2Ir2O7 reveals a continuous phase transition from a
paramagnetic metal to an antiferromagnetic insulator for a sample with
stoichiometry within ~1% resolution. The insulating phase has strong proximity
to an antiferromagnetic semimetal, which is stabilized by several % level of
the off-stoichiometry. Our observations suggest that in addition to electronic
correlation and spin-orbit coupling the magnetic order is essential for opening
the charge gap.Comment: 6 pages, 6 figure
Quantized spin Hall effect in Helium three-A and other p-wave paired Fermi systems
In this paper we propose the quantized spin Hall effect (SHE) in the vortex
state of a rotating p-wave paired Fermi system in an inhomogeneous magnetic
field and in a weak periodic potential. It is the three dimensional extension
of the spin Hall effect for a 3He-A superfluid film studied in Ref. [1]. It may
also be considered as a generalization of the 3D quantized charge Hall effect
of Bloch electrons in Ref. [2] to the spin transport. The A-phase of 3He or,
more generally, the p-wave paired phase of a cold Fermi atomic gas, under
suitable conditions should be a good candidate to observe the SHE, because the
system has a conserved spin current (with no spin-orbit couplings).Comment: 6 pages, revised version
Comment on “Collisionless shock and supernova remnant simulations on VULCAN” [Phys. Plasmas 8, 2439 (2001)]
This recent paper reports some real advances in experimental technique, but is misleading or incorrect in several places. First, the design assumes without discussion that the magnetic field will completely penetrate the plasma, but this is not likely. Second, when the magnetic field is present the surfaces of the converging plasmas will be Rayleigh–Taylor unstable. Third, any shocks produced in experiments like those reported may be collisionless but have no relevance to shocks in supernova remnants. Fourth, the experiment is not a meaningful hydrodynamic simulation of a supernova remnant. Finally, the hydrodynamic simulation results reported are also in error, leading to incorrect values for some scaling parameters. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69649/2/PHPAEN-9-2-727-1.pd
Some results on homoclinic and heteroclinic connections in planar systems
Consider a family of planar systems depending on two parameters and
having at most one limit cycle. Assume that the limit cycle disappears at some
homoclinic (or heteroclinic) connection when We present a method
that allows to obtain a sequence of explicit algebraic lower and upper bounds
for the bifurcation set The method is applied to two quadratic
families, one of them is the well-known Bogdanov-Takens system. One of the
results that we obtain for this system is the bifurcation curve for small
values of , given by . We obtain
the new three terms from purely algebraic calculations, without evaluating
Melnikov functions
Mesoscopic Stern-Gerlach spin filter by nonuniform spin-orbit interaction
A novel spin filtering in two-dimensional electron system with nonuniform
spin-orbit interactions (SOI) is theoretically studied. The strength of SOI is
modulated perpendicular to the charge current. A spatial gradient of effective
magnetic field due to the nonuniform SOI causes the Stern-Gerlach type spin
separation. The direction of the polarization is perpendicular to the current
and parallel to the spatial gradient. Almost 100 % spin polarization can be
realized even without applying any external magnetic fields and without
attaching ferromagnetic contacts. The spin polarization persists even in the
presence of randomness.Comment: 6 pages, 5 figures (2 color figures), to appear in Phys. Rev. B,
Rapid Commu
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