434 research outputs found
Hysteresis loops and adiabatic Landau-Zener-St\"uckelberg transitions in the magnetic molecule V
We have observed hysteresis loops and abrupt magnetization steps in the
magnetic molecule V, where each molecule comprises a pair of identical spin
triangles, in the temperature range 1-5 K for external magnetic fields with
sweep rates of several Tesla/ms executing a variety of closed cycles. The
hysteresis loops are accurately reproduced using a generalization of the Bloch
equation based on direct one-phonon transitions between the instantaneous
Zeeman-split levels of the ground state (an doublet) of each spin
triangle. The magnetization steps occur for and they are explained
in terms of adiabatic Landau-Zener-St\"{u}ckelberg transitions between the
lowest magnetic energy levels as modified by inter-triangle anisotropic
exchange of order 0.4 K.Comment: 4 pages, 3 figure
Anisotropic magnetic field responses of ferroelectric polarization in a trigonal multiferroic CuFe1-xAlxO2 (x=0.015)
We have investigated magnetic field dependences of a ferroelectric
incommensurate-helimagnetic order in a trigonal magneto-electric (ME)
multiferroic CuFe1-xAlxO2 with x=0.015, which exhibits the ferroelectric phase
as a ground state, by means of neutron diffraction, magnetization and
dielectric polarization measurements under magnetic fields applied along
various directions. From the present results, we have established the H-T
magnetic phase diagrams for the three principal directions of magnetic fields;
(i) parallel to the c axis, (ii) parallel to the helical axis, and (iii)
perpendicular to the c and the helical axes. While the previous dielectric
polarization (P) measurements on CuFe1-xGaxO2 with x=0.035 have demonstrated
that the magnetic field dependence of the `magnetic domain structure' results
in distinct magnetic field responses of P [S. Seki et al., Phys. Rev. Lett.,
103 237601 (2009)], the present study have revealed that the anisotropic
magnetic field dependence of the ferroelectric helimagnetic order `in each
magnetic domain' can be also a source of a variety of magnetic field responses
of P in CuFe1-xAxO2 systems (A=Al, Ga).Comment: 11 pages, 9 figures, accepted for publication in Phys. Rev.
Half-magnetization plateaux in Cr spinels
Magnetization plateaux, visible as anomalies in magnetic susceptibility at
low temperatures, are one of the hallmarks of frustrated magnetism. An
extremely robust half-magnetization plateau is observed in the spinel oxides
CdCr2O4 and HgCr2O4, where it is accompanied by a substantial lattice
distortion. We give an overview of the present state experiment for CdCr2O4 and
HgCr2O4, and show how such a half-magnetization plateau arises quite naturally
in a simple model of these systems, once coupling to the lattice is taken into
account.Comment: 8 pages latex using IOP macros, from review talk given at RHMF 2006
(Sendai
NAREOR: The Narrative Reordering Problem
Many implicit inferences exist in text depending on how it is structured that
can critically impact the text's interpretation and meaning. One such
structural aspect present in text with chronology is the order of its
presentation. For narratives or stories, this is known as the narrative order.
Reordering a narrative can impact the temporal, causal, event-based, and other
inferences readers draw from it, which in turn can have strong effects both on
its interpretation and interestingness. In this paper, we propose and
investigate the task of Narrative Reordering (NAREOR) which involves rewriting
a given story in a different narrative order while preserving its plot. We
present a dataset, NAREORC, with human rewritings of stories within ROCStories
in non-linear orders, and conduct a detailed analysis of it. Further, we
propose novel task-specific training methods with suitable evaluation metrics.
We perform experiments on NAREORC using state-of-the-art models such as BART
and T5 and conduct extensive automatic and human evaluations. We demonstrate
that although our models can perform decently, NAREOR is a challenging task
with potential for further exploration. We also investigate two applications of
NAREOR: generation of more interesting variations of stories and serving as
adversarial sets for temporal/event-related tasks, besides discussing other
prospective ones, such as for pedagogical setups related to language skills
like essay writing and applications to medicine involving clinical narratives.Comment: Accepted to AAAI 202
Electronic structure of pristine and K-doped solid picene: Non-rigid-band change and its implication for electron-intramolecular-vibration interaction
We use photoemission spectroscopy to study electronic structures of pristine
and K-doped solid picene. The valence band spectrum of pristine picene consists
of three main features with no state at the Fermi level (EF), while that of
K-doped picene has three structures similar to those of pristine picene with
new states near EF, consistent with the semiconductor-metal transition. The
K-induced change cannot be explained with a simple rigid-band model of pristine
picene, but can be interpreted by molecular orbital calculations considering
electron-intramolecular-vibration interaction. Excellent agreement of the
K-doped spectrum with the calculations points to importance of
electron-intramolecular-vibration interaction in K-doped picene.Comment: This article is accepted by Physical Review
Magnetization plateaux of S = 1/2 two-dimensional frustrated antiferromagnet CsCuBr
The field induced magnetic phase transitions of CsCuBr were
investigated by means of magnetization process and neutron scattering
experiments. This system undergoes magnetic phase transition at Ne\'{e}l
temperature K at zero field, and exhibits the magnetization
plateau at approximately one third of the saturation magnetization for the
field directions and . In the present study,
additional symptom of the two-third magnetization plateau was found in the
field derivative of the magnetization process. The magnetic structure was found
to be incommensurate with the ordering vector at
zero field. With increasing magnetic field parallel to the c-axis, the ordering
vector increases continuously and is locked at
in the plateau field range . This
indicates that the collinear \textit{up-up-down} spin structure is stabilized
by quantum fluctuation at the magnetization plateau.Comment: 6 pages, 4 Postscript figures, uses iopams.sty and IOPART.CL
Skyrmion in spinor condensates and its stability in trap potentials
A necessary condition for the existence of a skyrmion in two-component
Bose-Einstein condensates with symmetry was recently provided
by two of the authors [Phys. Rev. Lett. {\bf 97}, 080403 (2006)], by mapping
the problem to a classical particle in a potential subject to time-dependent
dissipation. Here we further elaborate this approach. For two classes of
models, we demonstrate the existence of the critical dissipation strength above
which the skyrmion solution does not exist. Furthermore, we discuss the local
stability of the skyrmion solution by considering the second-order variation. A
sufficient condition for the local stability is given in terms of the
ground-state energy of a one-dimensional quantum-mechanical Hamiltonian. This
condition requires a minimum number of bosons, for a certain class of the trap
potential. In the optimal case, the minimum number of bosons can be as small
.Comment: 12 pages, 9 figures, final versio
- …