13,516 research outputs found
Holographic classification of Topological Insulators and its 8-fold periodicity
Using generic properties of Clifford algebras in any spatial dimension, we
explicitly classify Dirac hamiltonians with zero modes protected by the
discrete symmetries of time-reversal, particle-hole symmetry, and chirality.
Assuming the boundary states of topological insulators are Dirac fermions, we
thereby holographically reproduce the Periodic Table of topological insulators
found by Kitaev and Ryu. et. al, without using topological invariants nor
K-theory. In addition we find candidate Z_2 topological insulators in classes
AI, AII in dimensions 0,4 mod 8 and in classes C, D in dimensions 2,6 mod 8.Comment: 19 pages, 4 Table
On the role of a new type of correlated disorder in extended electronic states in the Thue-Morse lattice
A new type of correlated disorder is shown to be responsible for the
appearance of extended electronic states in one-dimensional aperiodic systems
like the Thue-Morse lattice. Our analysis leads to an understanding of the
underlying reason for the extended states in this system, for which only
numerical evidence is available in the literature so far. The present work also
sheds light on the restrictive conditions under which the extended states are
supported by this lattice.Comment: 11 pages, LaTeX V2.09, 1 figure (available on request), to appear in
Physical Review Letter
First-Order Melting of a Moving Vortex Lattice: Effects of Disorder
We study the melting of a moving vortex lattice through numerical simulations
with the current driven 3D XY model with disorder. We find that there is a
first-order phase transition even for large disorder when the corresponding
equilibrium transition is continuous. The low temperature phase is an
anisotropic moving glass.Comment: Important changes from original version. Finite size analysis of
results has been added. Figure 2 has been changed. There is a new additional
Figure. To be published in Physical Review Letter
Synthetic Observations of Simulated Radio Galaxies I: Radio and X-ray Analysis
We present an extensive synthetic observational analysis of numerically-
simulated radio galaxies designed to explore the effectiveness of conventional
observational analyses at recovering physical source properties. These are the
first numerical simulations with sufficient physical detail to allow such a
study. The present paper focuses on extraction of magnetic field properties
from nonthermal intensity information. Synchrotron and inverse-Compton
intensities provided meaningful information about distributions and strengths
of magnetic fields, although considerable care was called for. Correlations
between radio and X-ray surface brightness correctly revealed useful dynamical
relationships between particles and fields. Magnetic field strength estimates
derived from the ratio of X-ray to radio intensity were mostly within about a
factor of two of the RMS field strength along a given line of sight. When
emissions along a given line of sight were dominated by regions close to the
minimum energy/equipartition condition, the field strengths derived from the
standard power-law-spectrum minimum energy calculation were also reasonably
close to actual field strengths, except when spectral aging was evident.
Otherwise, biases in the minimum- energy magnetic field estimation mirrored
actual differences from equipartition. The ratio of the inverse-Compton
magnetic field to the minimum-energy magnetic field provided a rough measure of
the actual total energy in particles and fields in most instances, within an
order of magnitude. This may provide a practical limit to the accuracy with
which one may be able to establish the internal energy density or pressure of
optically thin synchrotron sources.Comment: 43 pages, 14 figures; accepted for publication in ApJ, v601 n2
February 1, 200
Cosmic Rays Accelerated at Cosmological Shock Waves
Based on hydrodynamic numerical simulations and diffusive shock acceleration model, we calculated the ratio of cosmic ray (CR) to thermal energy. We found that the CR fraction can be less than similar to 0.1 in the intracluster medium, while it would be of order unity in the warm-hot intergalactic mediumopen2
Field-driven topological glass transition in a model flux line lattice
We show that the flux line lattice in a model layered HTSC becomes unstable
above a critical magnetic field with respect to a plastic deformation via
penetration of pairs of point-like disclination defects. The instability is
characterized by the competition between the elastic and the pinning energies
and is essentially assisted by softening of the lattice induced by a
dimensional crossover of the fluctuations as field increases. We confirm
through a computer simulation that this indeed may lead to a phase transition
from crystalline order at low fields to a topologically disordered phase at
higher fields. We propose that this mechanism provides a model of the low
temperature field--driven disordering transition observed in neutron
diffraction experiments on single crystals.Comment: 11 pages, 4 figures available upon request via snail mail from
[email protected]
Cosmological Shock Waves and Their Role in the Large Scale Structure of the Universe
We study the properties of cosmological shock waves identified in
high-resolution, N-body/hydrodynamic simulations of a CDM universe and
their role on thermalization of gas and acceleration of nonthermal, cosmic ray
(CR) particles. External shocks form around sheets, filaments and knots of mass
distribution when the gas in void regions accretes onto them. Within those
nonlinear structures, internal shocks are produced by infall of previously
shocked gas to filaments and knots, and during subclump mergers, as well as by
chaotic flow motions. Due to the low temperature of the accreting gas, the Mach
number of external shocks is high, extending up to or higher. In
contrast, internal shocks have mostly low Mach numbers. For all shocks of
the mean distance between shock surfaces over the entire computed
volume is Mpc at present, or Mpc for internal
shocks within nonlinear structures. Identified external shocks are more
extensive, with their surface area times larger than that of identified
internal shocks at present. However, especially because of higher preshock
densities, but also due to higher shock speeds, internal shocks dissipate more
energy. Hence, the internal shocks are mainly responsible for gas
thermalization as well as CR acceleration. In fact, internal shocks with 2 \la
M \la 4 contribute of the total dissipation. Using a nonlinear
diffusive shock acceleration model for CR protons, we estimate the ratio of CR
energy to gas thermal energy dissipated at cosmological shock waves to be
through the history of the universe. Our result supports scenarios in
which the intracluster medium contains energetically significant populations of
CRs.Comment: 25 pages, 8 figures including 1 in color. To appear in ApJ (v593 n2
August 20, 2003). Postscript file with full resolution
ftp://canopus.chungnam.ac.kr/ryu/cosmoshock.p
Dynamical Phase Transition in a Driven Disordered Vortex Lattice
Using Langevin dynamics, we have investigated the dynamics of vortices in a
disordered two dimensional superconductor subjected to a uniform driving
current. The results provide direct numerical evidence for a dynamical phase
transition between a plastic flow regime and a moving ``hexatic glass." The
simulated current-voltage characteristics are in excellent agreement with
recent transport measurements on amorphous thin film
superconductors.Comment: 13 pages, latex, revtex, 4 figures available upon request from
[email protected]
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