1,923 research outputs found
Quantum Mechanics, Common Sense and the Black Hole Information Paradox
The purpose of this paper is to analyse, in the light of information theory
and with the arsenal of (elementary) quantum mechanics (EPR correlations,
copying machines, teleportation, mixing produced in sub-systems owing to a
trace operation, etc.) the scenarios available on the market to resolve the
so-called black-hole information paradox. We shall conclude that the only
plausible ones are those where either the unitary evolution of quantum
mechanics is given up, in which information leaks continuously in the course of
black-hole evaporation through non-local processes, or those in which the world
is polluted by an infinite number of meta-stable remnants.Comment: 15 pages, Latex, CERN-TH.6889/9
Spiraling Solitons: a Continuum Model for Dynamical Phyllotaxis and Beyond
A novel, protean, topological soliton has recently been shown to emerge in
systems of repulsive particles in cylindrical geometries, whose statics is
described by the number-theoretical objects of phyllotaxis. Here we present a
minimal and local continuum model that can explain many of the features of the
phyllotactic soliton, such as locked speed, screw shift, energy transport and,
for Wigner crystal on a nanotube, charge transport. The treatment is general
and should apply to other spiraling systems. Unlike e.g. Sine-Gornon-like
systems, our solitons can exist between non-degenerate structure, imply a power
flow through the system, dynamics of the domains it separates; we also predict
pulses, both static and dynamic. Applications include charge transport in
Wigner Crystals on nanotubes or A- to B-DNA transitions.Comment: 8 Pages, 6 Figures, Phys Rev E in pres
Low Temperature Spin Freezing in Dy2Ti2O7 Spin Ice
We report a study of the low temperature bulk magnetic properties of the spin
ice compound Dy2Ti2O7 with particular attention to the (T < 4 K) spin freezing
transition. While this transition is superficially similar to that in a spin
glass, there are important qualitative differences from spin glass behavior:
the freezing temperature increases slightly with applied magnetic field, and
the distribution of spin relaxation times remains extremely narrow down to the
lowest temperatures. Furthermore, the characteristic spin relaxation time
increases faster than exponentially down to the lowest temperatures studied.
These results indicate that spin-freezing in spin ice materials represents a
novel form of magnetic glassiness associated with the unusual nature of
geometrical frustration in these materials.Comment: 24 pages, 8 figure
Coherent Behavior and Nonmagnetic Impurity Effects of the Spin Disordered State in NiGaS
Nonmagnetic impurity effects of the spin disordered state in the triangular
antiferromagnet NiGaS was studied through magnetic and thermal
measurements for NiZnGaS (0.0\le x\le 0.3). Only 1 %
substitution is enough to strongly suppress the coherence observed in the spin
disordered state. However, the suppression is not complete and the robust
feature of the T^2 dependent specific heat and its scaling behavior with the
Weiss temperature indicate the existence of a coherent Nambu-Goldstone mode.
Absence of either conventional magnetic order or bulk spin freezing suggests a
novel symmetry breaking of the ground state.Comment: 4 pages, 4 figure
Flux through a hole from a shaken granular medium
We have measured the flux of grains from a hole in the bottom of a shaken
container of grains. We find that the peak velocity of the vibration, vmax,
controls the flux, i.e., the flux is nearly independent of the frequency and
acceleration amplitude for a given value of vmax. The flux decreases with
increasing peak velocity and then becomes almost constant for the largest
values of vmax. The data at low peak velocity can be quantitatively described
by a simple model, but the crossover to nearly constant flux at larger peak
velocity suggests a regime in which the granular density near the container
bottom is independent of the energy input to the system.Comment: 14 pages, 4 figures. to appear in Physical Review
``Cosmological'' scenario for A-B phase transition in superfluid 3He
At a very rapid superfluid transition in He, follows after a reaction
with single neutron, the creation of topological defects (vortices) has
recently been demonstrated in accordance with the Kibble-Zurek scenario for the
cosmological analogue. We discuss here the extension of the Kibble-Zurek
scenario to the case when alternative symmetries may be broken and different
states nucleated independently. We have calculated the nucleation probability
of the various states of superfluid He during a superfluid transition. Our
results can explain the transition from supercooled phase to the phase,
triggered by nuclear reaction. The new scenario is an alternative to the
well-known ``baked Alaska'' scenario.Comment: RevTex file, 4 pages, 3 figures, submitted to Phys. Rev. Let
Temperature Dependence of the Magnetic Susceptibility for Triangular-Lattice Antiferromagnets with spatially anisotropic exchange constants
We present the temperature dependence of the uniform susceptibility of
spin-half quantum antiferromagnets on spatially anisotropic
triangular-lattices, using high temperature series expansions. We consider a
model with two exchange constants, and on a lattice that
interpolates between the limits of a square-lattice (), a
triangular-lattice (), and decoupled linear chains (). In all
cases, the susceptibility which has a Curie-Weiss behavior at high
temperatures, rolls over and begins to decrease below a peak temperature,
. Scaling the exchange constants to get the same peak temperature, shows
that the susceptibilities for the square-lattice and linear chain limits have
similar magnitudes near the peak. Maximum deviation arises near the
triangular-lattice limit, where frustration leads to much smaller
susceptibility and with a flatter temperature dependence. We compare our
results to the inorganic materials CsCuCl and CsCuBr and to a
number of organic molecular crystals. We find that the former (CsCuCl
and CsCuBr) are weakly frustrated and their exchange parameters
determined through the temperature dependence of the susceptibility are in
agreement with neutron-scattering measurements. In contrast, the organic
materials are strongly frustrated with exchange parameters near the isotropic
triangular-lattice limit.Comment: 10 pages, 9 figures and 1 table, revised versio
Diagnostic criterion for crystallized beams
Small ion crystals in a Paul trap are stable even in the absence of laser
cooling. Based on this theoretically and experimentally well-established fact
we propose the following diagnostic criterion for establishing the presence of
a crystallized beam: Absence of heating following the shut-down of all cooling
devices. The validity of the criterion is checked with the help of detailed
numerical simulations.Comment: REVTeX, 11 pages, 4 figures; submitted to PR
Low temperature spin fluctuations in geometrically frustrated Yb3Ga5O12
In the garnet structure compound Yb3Ga5O12, the Yb3+ ions (ground state
effective spin S' = 1/2) are situated on two interpenetrating corner sharing
triangular sublattices such that frustrated magnetic interactions are possible.
Previous specific heat measurements evidenced the development of short range
magnetic correlations below 0.5K and a lambda-transition at 54mK (Filippi et
al. J. Phys. C: Solid State Physics 13 (1980) 1277). From 170-Yb M"ossbauer
spectroscopy measurements down to 36mK, we find there is no static magnetic
order at temperatures below that of the lambda-transition. Below 0.3K, the
fluctuation frequency of the short range correlated Yb3+ moments progressively
slows down and as the temperature tends to 0, the frequency tends to a
quasi-saturated value of 3 x 10^9 s^-1. We also examined the Yb3+ paramagnetic
relaxation rates up to 300K using 172-Yb perturbed angular correlation
measurements: they evidence phonon driven processes.Comment: 6 pages, 5 figure
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