201 research outputs found
Field-Induced Transition on Triangular Plane in the Spin Ice Compound Dy2Ti2O7
The origin of the lowest-temperature anomaly reported several years ago using
a polycrystalline sample of the spin ice compound Dy2Ti2O7 had remained
unresolved. Here we finally clarify its origin by susceptibility measurements
down to 65 mK using single crystals under accurate control of the magnetic
fields in two independent directions. We demonstrate that the transition is
induced under a subtle field combination that precisely cancel the
nearest-neighbor spin interactions acting on the spins on the triangular
lattice within the pyrochlore structure. Contrary to the other two fieldinduced
transitions, this transition is driven only by the interactions beyond the
nearest neighbors. Our observation thus provides the first qualitative evidence
for the essential importance of the dipolar interaction beyond the nearest
neighbors in the spin ice.Comment: submitted to PR
Manfred and the Sublime
Dans sa DĂ©dicace Ă Don Juan (strophe 10), Byron sâexprime sur Milton en expliquant que le mot « Miltonique » est devenu synonyme du sublime Ă cause de la façon que choisissait de vivre Milton le poĂšte et lâhomme. Selon Byron, Milton est restĂ© fidĂšle Ă son crĂ©do politique et religieux malgrĂ© lâopposition de ses contemporains, suivant la Restauration. Aux yeux de Byron, il y a quelque chose de trĂšs sublime et grand dans la conduite de Milton, « le vieillard aveugle1 », qui vivait une situation difficile alors quâil Ă©tait « dĂ©fait, pĂąle et pauvre2 ». Cette perspective sur Milton rappelle une crĂ©ation de Byron, Manfred, qui reste fidĂšle Ă son crĂ©do jusquâĂ la fin et choisit de mourir plutĂŽt quâaccepter toute intervention du clergĂ© ou de lâĂglise qui puisse le sauver. Dans ses Observations sur le sentiment du beau et du sublime, Kant explique que lâhomme mĂ©lancolique « a surtout le sentiment du sublime3 ». On peut se demander si Kant expliquait certaines des caractĂ©ristiques du hĂ©ros de Byron. Il est certainement vrai que Manfred, comme Kant le souligne ailleurs, « brave le danger et mĂ©prise la mort ». Avant de mourir, il prononce ces derniers mots : « Vieillard! Ce nâest pas si difficile, mourir . . .4 » Ă cet Ă©gard, lâattitude du samurai japonais face Ă la vie et Ă la mort nous rappelle la notion du sublime. Le samurai est souvent prĂȘt Ă sâengager dans une bataille perdue dâavance et Ă y laisser sa vie afin de rester fidĂšle Ă son credo. Une telle attitude nous apparaĂźt « sublime ». Selon Kant, « soumettre ses passions par des principes est sublime ». Une autre caractĂ©ristique de Manfred en termes du concept du sublime repose sur le lieu dans lequel se dĂ©roule le drame, qui relĂšve du sublime Ă son tour. En effet, Byron choisit comme lieu de lâaction « les Hautes-Alpes5 ». Ainsi, on y trouve plusieurs scĂšnes que Burke et Kant pourraient appeler des exemples du « sublime-terrible ». Autrement dit, Manfred est une oeuvre dans laquelle le dĂ©cor et lâĂ©tat dâesprit du protagoniste peuvent ĂȘtre qualifiĂ©s de sublime
The "Coulomb phase" in frustrated systems
The "Coulomb phase" is an emergent state for lattice models (particularly
highly frustrated antiferromagnets) which have local constraints that can be
mapped to a divergence-free "flux". The coarse-grained version of this flux or
polarization behave analogously to electric or magnetic fields; in particular,
defects at which the local constraint is violated behave as effective charges
with Coulomb interactions. I survey the derivation of the characteristic
power-law correlation functions and the pinch-points in reciprocal space plots
of diffuse scattering, as well as applications to magnetic relaxation,
quantum-mechanical generalizations, phase transitions to long-range-ordered
states, and the effects of disorder.Comment: 30 pp, 5 figures (Sub. to Annual Reviews of Condensed Matter Physics
Adaptive Natural Language Generation for Task-oriented Dialogue via Reinforcement Learning
When a natural language generation (NLG) component is implemented in a
real-world task-oriented dialogue system, it is necessary to generate not only
natural utterances as learned on training data but also utterances adapted to
the dialogue environment (e.g., noise from environmental sounds) and the user
(e.g., users with low levels of understanding ability). Inspired by recent
advances in reinforcement learning (RL) for language generation tasks, we
propose ANTOR, a method for Adaptive Natural language generation for
Task-Oriented dialogue via Reinforcement learning. In ANTOR, a natural language
understanding (NLU) module, which corresponds to the user's understanding of
system utterances, is incorporated into the objective function of RL. If the
NLG's intentions are correctly conveyed to the NLU, which understands a
system's utterances, the NLG is given a positive reward. We conducted
experiments on the MultiWOZ dataset, and we confirmed that ANTOR could generate
adaptive utterances against speech recognition errors and the different
vocabulary levels of users.Comment: Accepted by COLING 202
Magnetodielectric Response of the Spin-Ice Dy2Ti2O7
We report the magneto-dielectric response of single crystals of the spin-ice
compound Dy2Ti2O7 down to 0.26 K. The dielectric constant under zero magnetic
field exhibits a clear decrease reflecting the development of the local
two-spins-in, two-spins-out structure below about 1.2 K. Both the real and
imaginary parts of the dielectric constant under magnetic fields sensitively
respond to various changes in the spin structures. We found that the real part
can be described in terms of local spin correlations among the moments of
tetrahedra, rather than among individual Dy3+ moments. Using the peaks in the
imaginary part, we have constructed a precise field-temperature phase diagram
in the [111] field direction. We thus demonstrate that the magneto-dielectric
response can be a high-sensitivity local probe of the spin state of
geometrically frustrated systems.Comment: 6 pages, 6 figure
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