1,034 research outputs found
Low-temperature ordered phases of the spin- XXZ chain system CsCoCl
In this study the magnetic order of the spin-1/2 XXZ chain system
CsCoCl in a temperature range from 50 mK to 0.5 K and in applied
magnetic fields up to 3.5 T is investigated by high-resolution measurements of
the thermal expansion and the specific heat. Applying magnetic fields along a
or c suppresses completely at about 2.1 T. In addition, we find
an adjacent intermediate phase before the magnetization saturates close to 2.5
T. For magnetic fields applied along b, a surprisingly rich phase diagram
arises. Two additional transitions are observed at critical fields T and T, which we propose to
arise from a two-stage spin-flop transition.Comment: 10 pages, 10 figure
Local Magnetization in the Boundary Ising Chain at Finite Temperature
We study the local magnetization in the 2-D Ising model at its critical
temperature on a semi-infinite cylinder geometry, and with a nonzero magnetic
field applied at the circular boundary of circumference . This model
is equivalent to the semi-infinite quantum critical 1-D transverse field Ising
model at temperature , with a symmetry-breaking field
applied at the point boundary. Using conformal field theory methods
we obtain the full scaling function for the local magnetization analytically in
the continuum limit, thereby refining the previous results of Leclair, Lesage
and Saleur in Ref. \onlinecite{Leclair}. The validity of our result as the
continuum limit of the 1-D lattice model is confirmed numerically, exploiting a
modified Jordan-Wigner representation. Applications of the result are
discussed.Comment: 9 pages, 3 figure
Information in Tullock contests
In Tullock contests in which the common value of the prize is uncertain and the
elasticity of the marginal cost of effort is increasing (decreasing), the effect of changes
of players’ information on the equilibrium efforts and payoffs is unambiguous: if
information is symmetric, then expected effort decreases (increases) as players become
better informed; in two-player contests, the expected effort of a player with information
advantage is less (greater) than that of his opponent. Sharper results arise when the
cost of effort is linear: Under symmetric information, expected effort and payoff are
invariant to changes in the players’ information. In two-player contests, both players
exert the same expected effort regardless of their information, although expected effort
is smaller when one player has information advantage than when both players have
the same information. Interestingly, the expected payoff of a player with information
advantage is larger than that of his opponent, even though he wins the prize less
frequently.Acknowledgments of financial support: Israel Science Foundation, Grant 648/2 (Einy); Ministerio Economía (Spain), Grants ECO2014-55953-P and MDM2014-0431, and Comunidad de Madrid, Grant S2015/HUM-3444 (Moreno)
Counting statistics in multiple path geometries and the fluctuations of the integrated current in a quantum stirring device
The amount of particles that are transported via a path of motion is
characterized by its expectation value and by its variance . We
analyze what happens if a particle has two optional paths available to get from
one site to another site, and in particular what is for the current
which is induced in a quantum stirring device. It turns out that coherent
splitting and the stirring effect are intimately related and cannot be
understood within the framework of the prevailing probabilistic theory.Comment: 11 pages, 2 figures, published version, Latex Eq# correcte
Statistical Physics of Fracture Surfaces Morphology
Experiments on fracture surface morphologies offer increasing amounts of data
that can be analyzed using methods of statistical physics. One finds scaling
exponents associated with correlation and structure functions, indicating a
rich phenomenology of anomalous scaling. We argue that traditional models of
fracture fail to reproduce this rich phenomenology and new ideas and concepts
are called for. We present some recent models that introduce the effects of
deviations from homogeneous linear elasticity theory on the morphology of
fracture surfaces, succeeding to reproduce the multiscaling phenomenology at
least in 1+1 dimensions. For surfaces in 2+1 dimensions we introduce novel
methods of analysis based on projecting the data on the irreducible
representations of the SO(2) symmetry group. It appears that this approach
organizes effectively the rich scaling properties. We end up with the
proposition of new experiments in which the rotational symmetry is not broken,
such that the scaling properties should be particularly simple.Comment: A review paper submitted to J. Stat. Phy
Peripheral fillings of relatively hyperbolic groups
A group theoretic version of Dehn surgery is studied. Starting with an
arbitrary relatively hyperbolic group we define a peripheral filling
procedure, which produces quotients of by imitating the effect of the Dehn
filling of a complete finite volume hyperbolic 3--manifold on the
fundamental group . The main result of the paper is an algebraic
counterpart of Thurston's hyperbolic Dehn surgery theorem. We also show that
peripheral subgroups of 'almost' have the Congruence Extension Property and
the group is approximated (in an algebraic sense) by its quotients obtained
by peripheral fillings. Various applications of these results are discussed.Comment: The difference with the previous version is that Proposition 3.2 is
proved for quasi--geodesics instead of geodesics. This allows to simplify the
exposition in the last section. To appear in Invent. Mat
Shot noise suppression at room temperature in atomic-scale Au junctions
Shot noise encodes additional information not directly inferable from simple
electronic transport measurements. Previous measurements in atomic-scale metal
junctions at cryogenic temperatures have shown suppression of the shot noise at
particular conductance values. This suppression demonstrates that transport in
these structures proceeds via discrete quantum channels. Using a high frequency
technique, we simultaneously acquire noise data and conductance histograms in
Au junctions at room temperature and ambient conditions. We observe noise
suppression at up to three conductance quanta, with possible indications of
current-induced local heating and noise in the contact region at high
biases. These measurements demonstrate the quantum character of transport at
room temperature at the atomic scale. This technique provides an additional
tool for studying dissipation and correlations in nanodevices.Comment: 15 pages, 4 figures + supporting information (6 pages, 6 figures
Velocity correlations in granular materials
A system of inelastic hard disks in a thin pipe capped by hot walls is
studied with the aim of investigating velocity correlations between particles.
Two effects lead to such correlations: inelastic collisions help to build
localized correlations, while momentum conservation and diffusion produce long
ranged correlations. In the quasi-elastic limit, the velocity correlation is
weak, but it is still important since it is of the same order as the deviation
from uniformity. For system with stronger inelasticity, the pipe contains a
clump of particles in highly correlated motion. A theory with empirical
parameters is developed. This theory is composed of equations similar to the
usual hydrodynamic laws of conservation of particles, energy, and momentum.
Numerical results show that the theory describes the dynamics satisfactorily in
the quasi-elastic limit, however only qualitatively for stronger inelasticity.Comment: 12 pages (REVTeX), 15 figures (Postscript). submitted to Phys. Rev.
On the algorithmic construction of classifying spaces and the isomorphism problem for biautomatic groups
We show that the isomorphism problem is solvable in the class of central
extensions of word-hyperbolic groups, and that the isomorphism problem for
biautomatic groups reduces to that for biautomatic groups with finite centre.
We describe an algorithm that, given an arbitrary finite presentation of an
automatic group , will construct explicit finite models for the skeleta
of and hence compute the integral homology and cohomology of
.Comment: 21 pages, 4 figure
- …