723 research outputs found
Dynamical magneto-electric coupling in helical magnets
Collective mode dynamics of the helical magnets coupled to electric
polarization via spin-orbit interaction is studied theoretically. The soft
modes associated with the ferroelectricity are not the transverse optical
phonons, as expected from the Lyddane-Sachs-Teller relation, but are the spin
waves hybridized with the electric polarization. This leads to the Drude-like
dielectric function in the limit of zero magnetic
anisotropy. There are two more low-lying modes; phason of the spiral and
rotation of helical plane along the polarization axis. The roles of these soft
modes in the neutron scattering and antiferromagnetic resonance are revealed,
and a novel experiment to detect the dynamical magneto-electric coupling is
proposed.Comment: 5 pages, 1 figur
Role of the Dzyaloshinskii-Moriya interaction in multiferroic perovskites
With the perovskite multiferroic RMnO3 (R = Gd, Tb, Dy) as guidance, we argue
that the Dzyaloshinskii-Moriya interaction (DMI) provides the microscopic
mechanism for the coexistence and strong coupling between ferroelectricity and
incommensurate magnetism. We use Monte-Carlo simulations and zero temperature
exact calculations to study a model incorporating the double-exchange,
superexchange, Jahn-Teller and DMI terms. The phase diagram contains a
multiferroic phase between A and E antiferromagnetic phases, in excellent
agreement with experiments.Comment: 6 pages, 5 figure
Charged pions from Ni on Ni collisions between 1 and 2 AGeV
Charged pions from Ni + Ni reactions at 1.05, 1.45 and 1.93 AGeV are measured
with the FOPI detector. The mean multiplicities per mean number of
participants increase with beam energy, in accordance with earlier studies of
the Ar + KCl and La + La systems. The pion kinetic energy spectra have concave
shape and are fitted by the superposition of two Boltzmann distributions with
different temperatures. These apparent temperatures depend only weakly on
bombarding energy. The pion angular distributions show a forward/backward
enhancement at all energies, but not the enhancement which was
observed in case of the Au + Au system. These features also determine the
rapidity distributions which are therefore in disagreement with the hypothesis
of one thermal source. The importance of the Coulomb interaction and of the
pion rescattering by spectator matter in producing these phenomena is
discussed.Comment: 22 pages, Latex using documentstyle[12pt,a4,epsfig], to appear in Z.
Phys.
Spin dynamics of the quasi two dimensional spin-1/2 quantum magnet Cs_2CuCl_4
We study dynamical properties of the anisotropic triangular quantum
antiferromagnet Cs_2CuCl_4. Inelastic neutron scattering measurements have
established that the dynamical spin correlations cannot be understood within a
linear spin wave analysis. We go beyond linear spin wave theory by taking
interactions between magnons into account in a 1/S expansion. We determine the
dynamical structure factor and carry out extensive comparisons with
experimental data. We find that compared to linear spin wave theory a
significant fraction of the scattering intensity is shifted to higher energies
and strong scattering continua are present. However, the 1/S expansion fails to
account for the experimentally observed large quantum renormalization of the
exchange energies.Comment: 13 pages, 11 figures, higher quality figures can be obtained from the
author
Helimagnon Bands as Universal Spin Excitations of Chiral Magnets
MnSi is a cubic compound with small magnetic anisotropy, which stabilizes a
helimagnetic spin spiral that reduces to a ferromagnetic and antiferromagnetic
state in the long- and short-wavelength limit, respectively. We report a
comprehensive inelastic neutron scattering study of the collective magnetic
excitations in the helimagnetic state of MnSi. In our study we observe a rich
variety of seemingly anomalous excitation spectra, as measured in well over
twenty different locations in reciprocal space. Using a model based on only
three parameters, namely the measured pitch of the helix, the measured
ferromagnetic spin wave stiffness and the amplitude of the signal, as the only
free variable, we can simultaneously account for \textit{all} of the measured
spectra in excellent quantitative agreement with experiment. Our study
identifies the formation of intense, strongly coupled bands of helimagnons as a
universal characteristic of systems with weak chiral interactions.Comment: 8 pages, 4 figures, references updated, introduction updated,
reformatte
Plans for Hadronic Structure Studies at J-PARC
Hadron-physics projects at J-PARC are explained. The J-PARC is the
most-intense hadron-beam facility in the multi-GeV high-energy region. By using
secondary beams of kaons, pions, and others as well as the primary-beam proton,
various hadron projects are planned. First, some of approved experiments are
introduced on strangeness hadron physics and hadron-mass modifications in
nuclear medium. Second, future possibilities are discussed on hadron-structure
physics, including structure functions of hadrons, spin physics, and
high-energy hadron reactions in nuclear medium. The second part is discussed in
more details because this is an article in the hadron-structure session.Comment: 10 pages, LaTeX, 20 eps files, to be published in Journal of Physics:
Conference Series (JPCS), Proceedings of the 24th International Nuclear
Physics Conference (INPC 2010), Vancouver, Canada, July 4 - 9, 201
Ground states of a frustrated spin-1/2 antifferomagnet: Cs_2CuCl_4 in a magnetic field
We present detailed calculations of the magnetic ground state properties of
CsCuCl in an applied magnetic field, and compare our results with
recent experiments. The material is described by a spin Hamiltonian, determined
with precision in high field measurements, in which the main interaction is
antiferromagnetic Heisenberg exchange between neighboring spins on an
anisotropic triangular lattice. An additional, weak Dzyaloshinkii-Moriya
interaction introduces easy-plane anisotropy, so that behavior is different for
transverse and longitudinal field directions. We determine the phase diagram as
a function of field strength for both field directions at zero temperature,
using a classical approximation as a first step. Building on this, we calculate
the effect of quantum fluctuations on the ordering wavevector and components of
the ordered moments, using both linear spinwave theory and a mapping to a Bose
gas which gives exact results when the magnetization is almost saturated. Many
aspects of the experimental data are well accounted for by this approach.Comment: 13 Pages, 9 Figure
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