2,011 research outputs found
Phase-resolved Spin-Wave Tomography
The propagation dynamics of spin waves are represented by their dispersion
relations. Recently, we have developed a method, called spin-wave tomography
(SWaT), to obtain dispersion relation of spin waves in the long wavelength
regime, so-called pure magnetostatic waves. In our previous studies on SWaT,
phase information of spin waves was disregarded. In this report, we demonstrate
an advanced SWaT analysis, called phase-resolved spin-wave tomography (PSWaT),
to realize the direct observation of the amplitude and the phase of spin waves.
The PSWaT spectra are obtained by separating the real and the imaginary
components of the complex Fourier transform in the SWaT analysis. We
demonstrate the PSWaT spectra of spin waves excited by the photo-induced
demagnetization in a Bi-doped garnet film, reflecting the characteristic
features of the complex dynamical susceptibility affected by magnetostatic
coupling in the film.Comment: 5 pages, 4 figure
Spin-glass transition in bond-disordered Heisenberg antiferromagnets coupled with local lattice distortions on a pyrochlore lattice
Motivated by puzzling characteristics of spin-glass transitions widely
observed in pyrochlore-based frustrated materials, we investigate effects of
coupling to local lattice distortions in a bond-disordered antiferromagnet on
the pyrochlore lattice by extensive Monte Carlo simulations. We show that the
spin-glass transition temperature \TSG is largely enhanced by the
spin-lattice coupling, and furthermore, becomes almost independent of
in a wide range of the disorder strength . The critical property of the
spin glass transition is indistinguishable from that of the canonical
Heisenberg spin glass in the entire range of . These peculiar behaviors
are ascribed to a modification of the degenerate manifold from continuous to
semidiscrete one by the spin-lattice coupling.Comment: 4 pages, 3 figures, major revisions, accepted for publication in PR
Casimir interaction among heavy fermions in the BCS-BEC crossover
We investigate a two-species Fermi gas with a large mass ratio interacting by
an interspecies short-range interaction. Using the Born-Oppenheimer
approximation, we determine the interaction energy of two heavy fermions
immersed in the Fermi sea of light fermions as a function of the s-wave
scattering length. In the BCS limit, we recover the perturbative calculation of
the effective interaction between heavy fermions. The p-wave projection of the
effective interaction is attractive in the BCS limit while it turns out to be
repulsive near the unitarity limit. We find that the p-wave attraction reaches
its maximum between the BCS and unitarity limits, where the maximal p-wave
pairing of heavy minority fermions is expected. We also investigate the case
where the heavy fermions are confined in two dimensions and the p-wave
attraction between them is found to be stronger than that in three dimensions.Comment: 11 pages, 6 figure
Frequency and wavenumber selective excitation of spin waves through coherent energy transfer from elastic waves
Using spin-wave tomography (SWaT), we have investigated the excitation and
the propagation dynamics of optically-excited magnetoelastic waves, i.e.
hybridized modes of spin waves and elastic waves, in a garnet film. By using
time-resolved SWaT, we reveal the excitation dynamics of magnetoelastic waves
through coherent-energy transfer between optically-excited pure-elastic waves
and spin waves via magnetoelastic coupling. This process realizes frequency and
wavenumber selective excitation of spin waves at the crossing of the dispersion
relations of spin waves and elastic waves. Finally, we demonstrate that the
excitation mechanism of the optically-excited pure-elastic waves, which are the
source of the observed magnetoelastic waves, is dissipative in nature.Comment: 5 pages, 4 figure
Critical property of spin-glass transition in a bond-disordered classical antiferromagnetic Heisenberg model with a biquadratic interaction
Motivated by puzzling spin-glass behaviors observed in many pyrochlore-based
magnets, effects of magnetoelastic coupling to local lattice distortions were
recently studied by the authors for a bond-disordered antiferromagnet on a
pyrochlore lattice [Phys. Rev. Lett. 107, 047204 (2011)]. Here, we extend the
analyses with focusing on the critical property of the spin-glass transition
which occurs concomitantly with a nematic transition. Finite-size scaling
analyses are performed up to a larger system size with 8192 spins to estimate
the transition temperature and critical exponents. The exponents are compared
with those in the absence of the magnetoelastic coupling and with those for the
canonical spin-glass systems. We also discuss the temperature dependence of the
specific heat in comparison with that in canonical spin-glass systems as well
as an experimental result.Comment: 4 pages, 2 figures, proceedings for LT2
Comparing simulated Al maps to gamma-ray measurements
© ESO 2019.Context. The diffuse gamma-ray emission of at 1.8 MeV reflects ongoing nucleosynthesis in the Milky Way, and traces massive-star feedback in the interstellar medium due to its 1 Myr radioactive lifetime. Interstellar-medium morphology and dynamics are investigated in astrophysics through 3D hydrodynamic simulations in fine detail, as only few suitable astronomical probes are available. Aims. We compare a galactic-scale hydrodynamic simulation of the Galaxy's interstellar medium, including feedback and nucleosynthesis, with gamma-ray data on emission in the Milky Way extracting constraints that are only weakly dependent on the particular realisation of the simulation or Galaxy structure. Methods. Due to constraints and biases in both the simulations and the gamma-ray observations, such comparisons are not straightforward. For a direct comparison, we perform maximum likelihood fits of simulated sky maps as well as observation-based maximum entropy maps to measurements with INTEGRAL/SPI. To study general morphological properties, we compare the scale heights of emission produced by the simulation to INTEGRAL/SPI measurements.} Results. The direct comparison shows that the simulation describes the observed inner Galaxy well, but differs significantly from the observed full-sky emission morphology. Comparing the scale height distribution, we see similarities for small scale height features and a mismatch at larger scale heights. We attribute this to the prominent foreground emission sites that are not captured by the simulation.Peer reviewedFinal Accepted Versio
180-degree phase shift of magnetoelastic waves observed by phase-resolved spin-wave tomography
We have investigated optically-excited magnetoelastic waves by phase-resolved
spin-wave tomography (PSWaT). PSWaT reconstructs dispersion relation of spin
waves together with their phase information by using time-resolved
magneto-optical imaging for spin-wave propagation followed by an analysis based
on the convolution theorem and a complex Fourier transform. In PSWaT spectra
for a Bi-doped garnet film, we found a 180 degree phase shift of magnetoelastic
waves at around the crossing of the dispersion relations of spin and elastic
waves. The result is explained by a coupling between spin waves and elastic
waves through magnetoelastic interaction. We also propose an efficient way for
phase manipulation of magnetoelastic waves by rotating the orientation of
magnetization less than 10 degree.Comment: 5 pages, 4 figure
The mapping class group and the Meyer function for plane curves
For each d>=2, the mapping class group for plane curves of degree d will be
defined and it is proved that there exists uniquely the Meyer function on this
group. In the case of d=4, using our Meyer function, we can define the local
signature for 4-dimensional fiber spaces whose general fibers are
non-hyperelliptic compact Riemann surfaces of genus 3. Some computations of our
local signature will be given.Comment: 24 pages, typo adde
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