5,924 research outputs found

### Universality and Scaling Behaviour of Injected Power in Elastic Turbulence in Worm-like Micellar Gel

We study the statistical properties of spatially averaged global injected
power fluctuations for Taylor-Couette flow of a worm-like micellar gel formed
by surfactant CTAT. At sufficiently high Weissenberg numbers (Wi) the shear
rate and hence the injected power p(t) at a constant applied stress shows large
irregular fluctuations in time. The nature of the probability distribution
function (pdf) of p(t) and the power-law decay of its power spectrum are very
similar to that observed in recent studies of elastic turbulence for polymer
solutions. Remarkably, these non-Gaussian pdfs can be well described by an
universal large deviation functional form given by the Generalized Gumbel (GG)
distribution observed in the context of spatially averaged global measures in
diverse classes of highly correlated systems. We show by in-situ rheology and
polarized light scattering experiments that in the elastic turbulent regime the
flow is spatially smooth but random in time, in agreement with a recent
hypothesis for elastic turbulence.Comment: 8 pages, 3 figure

### Ground state of an $S=1/2$ distorted diamond chain - model of $\rm Cu_3 Cl_6 (H_2 O)_2 \cdot 2H_8 C_4 SO_2$

We study the ground state of the model Hamiltonian of the trimerized $S=1/2$
quantum Heisenberg chain $\rm Cu_3 Cl_6 (H_2 O)_2 \cdot 2H_8 C_4 SO_2$ in which
the non-magnetic ground state is observed recently. This model consists of
stacked trimers and has three kinds of coupling constants between spins; the
intra-trimer coupling constant $J_1$ and the inter-trimer coupling constants
$J_2$ and $J_3$. All of these constants are assumed to be antiferromagnetic. By
use of the analytical method and physical considerations, we show that there
are three phases on the $\tilde J_2 - \tilde J_3$ plane ($\tilde J_2 \equiv
J_2/J_1$, $\tilde J_3 \equiv J_3/J_1$), the dimer phase, the spin fluid phase
and the ferrimagnetic phase. The dimer phase is caused by the frustration
effect. In the dimer phase, there exists the excitation gap between the
two-fold degenerate ground state and the first excited state, which explains
the non-magnetic ground state observed in $\rm Cu_3 Cl_6 (H_2 O)_2 \cdot 2H_8
C_4 SO_2$. We also obtain the phase diagram on the $\tilde J_2 - \tilde J_3$
plane from the numerical diagonalization data for finite systems by use of the
Lanczos algorithm.Comment: LaTeX2e, 15 pages, 21 eps figures, typos corrected, slightly detailed
explanation adde

### Universality in the entanglement structure of ferromagnets

Systems of exchange-coupled spins are commonly used to model ferromagnets.
The quantum correlations in such magnets are studied using tools from quantum
information theory. Isotropic ferromagnets are shown to possess a universal
low-temperature density matrix which precludes entanglement between spins, and
the mechanism of entanglement cancellation is investigated, revealing a core of
states resistant to pairwise entanglement cancellation. Numerical studies of
one-, two-, and three-dimensional lattices as well as irregular geometries
showed no entanglement in ferromagnets at any temperature or magnetic field
strength.Comment: 4 pages, 2 figure

### Spin Gap of Two-Dimensional Antiferromagnet Representing CaV$_4$O$_9$

We examined a two-dimensional Heisenberg model with two kinds of exchange
energies, $J_e$ and $J_c$. This model describes localized spins at vanadium
ions in a layer of CaV$_4$O$_9$, for which a spin gap is found by a recent
experiment. Comparing the high temperature expansion of the magnetic
susceptibility to experimental data, we determined the exchange energies as
$J_e \simeq$ 610 K and $J_c \simeq$ 150 K. By the numerical diagonalization we
estimated the spin gap as $\Delta \sim 0.2J_e \simeq$ 120 K, which consists
with the experimental value 107 K. Frustration by finite $J_c$ enhances the
spin gap.Comment: 12 pages of LaTex, 4 figures availavule upon reques

### A chiral spin liquid wave function and the Lieb-Schulz-Mattis theorem

We study a chiral spin liquid wave function defined as a Gutwziller projected
BCS state with a complex pairing function. After projection, spontaneous
dimerization is found for any odd but finite number of chains, thus satisfying
the Lieb-Schultz-Mattis theorem, whereas for even number of chains there is no
dimerization. The two-dimensional thermodynamic limit is consistently reached
for large number of chains since the dimer order parameter vanishes in this
limit. This property clearly supports the possibility of a spin liquid ground
state in two dimensions with a gap to all {\em physical} excitations and with
no broken translation symmetry.Comment: 4 pages, 4 picture

### Magnetic Order Beyond RKKY in the Classical Kondo Lattice

We study the Kondo lattice model of band electrons coupled to classical
spins, in three dimensions, using a combination of variational calculation and
Monte Carlo. We use the weak coupling `RKKY' window and the strong coupling
regime as benchmarks, but focus on the physically relevant intermediate
coupling regime. Even for modest electron-spin coupling the phase boundaries
move away from the RKKY results, the non interacting Fermi surface no longer
dictates magnetic order, and weak coupling `spiral' phases give way to
collinear order. We use these results to revisit the classic problem of 4f
magnetism and demonstrate how both electronic structure and coupling effects
beyond RKKY control the magnetism in these materials.Comment: 6 pages, 4 figs. Improved figures, expanded captions. To appear in
Europhys. Let

### Schwarzschild horizon dynamics and SU(2) Chern-Simons theory

We discuss the effect of different choices in partial gauge fixing of bulk
local Lorentz invariance, on the description of the horizon degrees of freedom
of a Schwarzschild black hole as an SU(2) Chern-Simons theory with specific
sources. A classically equivalent description in terms of an ISO(2)
Chern-Simons theory is also discussed. Further, we demonstrate that both these
descriptions can be partially gauge fixed to a horizon theory with U(1) local
gauge invariance, with the solder form sources being subject to extra
constraints in directions orthogonal to an internal vector field left invariant
by U(1) transformations. Seemingly disparate approaches on characterization of
the horizon theory for the Schwarzschild black hole (as well as spherical
Isolated Horizons in general) are thus shown to be equivalent physically.Comment: 22 pages Latex, no figures, version accepted for publication in
Physical Review

### A non-Hermitian critical point and the correlation length of strongly correlated quantum systems

We study a non-Hermitian generalization of quantum systems in which an
imaginary vector potential is added to the momentum operator. In the
tight-binding approximation, we make the hopping energy asymmetric in the
Hermitian Hamiltonian. In a previous article, we conjectured that the
non-Hermitian critical point where the energy gap vanishes is equal to the
inverse correlation length of the Hermitian system and we confirmed the
conjecture for two exactly solvable systems. In this article, we present more
evidence for the conjecture. We also argue the basis of our conjecture by
noting the dispersion relation of the elementary excitation.Comment: 25 pages, 18 figure

### Exact solution of a model of time-dependent evolutionary dynamics in a rugged fitness landscape

A simplified form of the time dependent evolutionary dynamics of a
quasispecies model with a rugged fitness landscape is solved via a mapping onto
a random flux model whose asymptotic behavior can be described in terms of a
random walk. The statistics of the number of changes of the dominant genotype
from a finite set of genotypes are exactly obtained confirming existing
conjectures based on numerics.Comment: 5 pages RevTex 2 figures .ep

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