12,489 research outputs found
Theory of spin current in chiral helimagnet
We give detailed description of the transport spin current in the chiral
helimagnet. Under the static magnetic field applied perpendicular to the
helical axis, the magnetic kink crystal (chiral soliton lattice) is formed.
Once the kink crystal begins to move under the Galilean boost, the spin-density
accumulation occurs inside each kink and there emerges periodic arrays of the
induced magnetic dipoles carrying the transport spin current. The coherent
motion of the kink crystal dynamically generates the spontaneous
demagnetization field. This mechanism is analogous to the
D\"{o}ring-Becker-Kittel mechanism of the domain wall motion in ferromagnets.
To describe the kink crystal motion, we took account of not only the tangential
-fluctuations but the longitudinal -fluctuations around the
helimagnetic configuration. Based on the collective coordinate method and the
Dirac's canonical formulation for the singular Lagrangian system, we derived
the closed formulae for the mass, spin current and induced magnetic dipole
moment accompanied with the kink crystal motion. To materialize the theoretical
model presented here, symmetry-adapted material synthesis would be required,
where the interplay of crystallographic and magnetic chirality plays a key role
there.Comment: 16 pages, 6 figures, to be published in Phys. Rev.
Interchain Coupling Effects and Solitons in CuGeO_3
The effects of interchain coupling on solitons and soliton lattice structures
in CuGeO3 are explored. It is shown that interchain coupling substantially
increases the soliton width and changes the soliton lattice structures in the
incommensurate phase. It is proposed that the experimentally observed large
soliton width in CuGeO3 is mainly due to interchain coupling effects.Comment: 4 pages, LaTex, one eps figure included. No essential changes except
forma
Functional renormalization-group approach to the Pokrovsky-Talapov model via modified massive Thirring fermion model
A possibility of the topological Kosterlitz-Thouless~(KT) transition in the
Pokrovsky-Talapov~(PT) model is investigated by using the functional
renormalization-group (RG) approach by Wetterich. Our main finding is that the
nonzero misfit parameter of the model, which can be related with the linear
gradient term (Dzyaloshinsky-Moriya interaction), makes such a transition
impossible, what contradicts the previous consideration of this problem by
non-perturbative RG methods. To support the conclusion the initial PT model is
reformulated in terms of the 2D theory of relativistic fermions using an
analogy between the 2D sine-Gordon and the massive Thirring models. In the new
formalism the misfit parameter corresponds to an effective gauge field that
enables to include it in the RG procedure on an equal footing with the other
parameters of the theory. The Wetterich equation is applied to obtain flow
equations for the parameters of the new fermionic action. We demonstrate that
these equations reproduce the KT type of behavior if the misfit parameter is
zero. However, any small nonzero value of the quantity rules out a possibility
of the KT transition. To confirm the finding we develop a description of the
problem in terms of the 2D Coulomb gas model. Within the approach the breakdown
of the KT scenario gains a transparent meaning, the misfit gives rise to an
effective in-plane electric field that prevents a formation of bound
vortex-antivortex pairs.Comment: 12 pages, 3 figure
Direct detection of the relative strength of Rashba and Dresselhaus spin-orbit interaction: Utilizing the SU(2) symmetry
We propose a simple method to detect the relative strength of Rashba and
Dresselhaus spin-obit interactions in quantum wells (QWs) without relying on
the directional-dependent physical quantities. This method utilize the
asymmetry of critical gate voltages that leading to the remarkable signals of
SU(2) symmetry, which happens to reflect the intrinsic structure inversion
asymmetry of the QW. We support our proposal by the numerical calculation of
in-plane relaxation times based on the self-consistent eight-band Kane model.
We find that the two different critical gate voltages leading to the maximum
spin relaxation times [one effect of the SU(2) symmetry] can simply determine
the ratio of the coefficients of Rashba and Dresselhaus terms. Our proposal can
also be generalized to extract the relative strengths of the spin-orbit
interactions in quantum wire and quantum dot structures.Comment: 5 pages, 4 figure
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
4p states and X-Ray Spectroscopy
The 4p states in transition metals and their compounds usually play minor
roles on their physical quantities. Recent development of resonant x-ray
scattering (RXS) at the K-edge of transition metals, however, casts light on
the 4p states, because the signals on orbital and magnetic superlattice spots
are brought about by the modulation in the 4p states. The 4p states are
extending in solids and thereby sensitive to electronic states at neighboring
sites. This characteristic determines the mechanism of RXS that the intensity
on the orbital superlattice spots are mainly generated by the lattice
distortion and those on magnetic superlattice spots by the coupling of the 4p
states with the orbital polarization in the 3d states at neighboring sites.
Taking up typical examples for orbital and magnetic RXS, we demonstrate these
mechanisms on the basis of the band structure calculation. Finally, we study
the MCD spectra at the K-edge, demonstrating that the same mechanism as the
magnetic RXS is working.Comment: 9 pages, 9 figures, submitted to Physica Scripta (comment
Theory of magnetoelastic resonance in a mono-axial chiral helimagnet
We study magnetoelastic resonance phenomena in a mono-axial chiral helimagnet
belonging to hexagonal crystal class. By computing the spectrum of coupled
elastic wave and spin wave, it is demonstrated how hybridization occurs
depending on their chirality. Specific features of the magnetoelastic resonance
are discussed for the conical phase and the soliton lattice phase stabilized in
the mono-axial chiral helimagnet. The former phase exhibits appreciable
non-reciprocity of the spectrum, the latter is characterized by a
multi-resonance behavior. We propose that the non-reciprocal spin wave around
the forced-ferromagnetic state has potential capability to convert the linearly
polarized elastic wave to circularly polarized one with the chirality opposite
to the spin wave chirality.Comment: 12 pages, 5 figures, Accepted in Phys. Rev.
The role of the resonance in the reaction
We investigate the photo-production in the reaction within the effective Lagrangian method near
threshold. In addition to the "background" contributions from the contact,
channel exchange, and channel nucleon pole terms, which were
already considered in previous works, the contribution from the nucleon
resonance (spin-parity ) is also considered. We show
that the inclusion of the nucleon resonance leads to a fairly good
description of the new LEPS differential cross section data, and that these
measurements can be used to determine some of the properties of this latter
resonance. However, serious discrepancies appear when the predictions of the
model are compared to the photon-beam asymmetry also measured by the LEPS
Collaboration.Comment: 9 pages,6 figures, 1 tabl
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
Transport magnetic currents driven by moving kink crystal in chiral helimagnets
We show that the bulk transport magnetic current is generated by the moving
magnetic kink crystal (chiral soliton lattice) formed in the chiral helimagnet
under the static magnetic field applied perpendicular to the helical axis. The
current is caused by the non-equilibrium transport momentum with the kink mass
being determined by the spin fluctuations around the kink crystal state. An
emergence of the transport magnetic currents is then a consequence of the
dynamical off-diagonal long range order along the helical axis. We derive an
explicit formula for the inertial mass of the kink crystal and the current in
the weak field limit.Comment: 5 pages, 3 figures, to appear in Phys. Rev.
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