582 research outputs found
Preroughening, Diffusion, and Growth of An FCC(111) Surface
Preroughening of close-packed fcc(111) surfaces, found in rare gas solids, is
an interesting, but poorly characterized phase transition. We introduce a
restricted solid-on-solid model, named FCSOS, which describes it. Using mostly
Monte Carlo, we study both statics, including critical behavior and scattering
properties, and dynamics, including surface diffusion and growth. In antiphase
scattering, it is shown that preroughening will generally show up at most as a
dip. Surface growth is predicted to be continuous at preroughening, where
surface self-diffusion should also drop. The physical mechanism leading to
preroughening on rare gas surfaces is analysed, and identified in the step-step
elastic repulsion.Comment: Revtex + uuencoded figures, to appear in Physical Review Letter
Crossover from Isotropic to Directed Percolation
Directed percolation is one of the generic universality classes for dynamic
processes. We study the crossover from isotropic to directed percolation by
representing the combined problem as a random cluster model, with a parameter
controlling the spontaneous birth of new forest fires. We obtain the exact
crossover exponent at using Coulomb gas methods in 2D.
Isotropic percolation is stable, as is confirmed by numerical finite-size
scaling results. For , the stability seems to change. An intuitive
argument, however, suggests that directed percolation at is unstable and
that the scaling properties of forest fires at intermediate values of are
in the same universality class as isotropic percolation, not only in 2D, but in
all dimensions.Comment: 4 pages, REVTeX, 4 epsf-emedded postscript figure
Roughening Induced Deconstruction in (100) Facets of CsCl Type Crystals
The staggered 6-vertex model describes the competition between surface
roughening and reconstruction in (100) facets of CsCl type crystals. Its phase
diagram does not have the expected generic structure, due to the presence of a
fully-packed loop-gas line. We prove that the reconstruction and roughening
transitions cannot cross nor merge with this loop-gas line if these degrees of
freedom interact weakly. However, our numerical finite size scaling analysis
shows that the two critical lines merge along the loop-gas line, with strong
coupling scaling properties. The central charge is much larger than 1.5 and
roughening takes place at a surface roughness much larger than the conventional
universal value. It seems that additional fluctuations become critical
simultaneously.Comment: 31 pages, 9 figure
Nonlinear sigma model study of a frustrated spin ladder
A model of two-leg spin-S ladder with two additional frustrating diagonal
exchange couplings J_{D}, J_{D}' is studied within the framework of the
nonlinear sigma model approach. The phase diagram has a rich structure and
contains 2S gapless phase boundaries which split off the boundary to the fully
saturated ferromagnetic phase when J_{D} and J_{D}' become different. For the
S=1/2 case, the phase boundaries are identified as separating two topologically
distinct Haldane-type phases discussed recently by Kim et al.
(cond-mat/9910023).Comment: revtex 4 pages, figures embedded (psfig
Ferrimagnetic and Long Period Antiferromagnetic Phases in High Spin Heisenberg Chains with D-Modulation
The ground state properties of the high spin Heisenberg chains with
alternating single site anisotropy are investigated by means of the numerical
exact daigonaization and DMRG method. It is found that the ferrimagnetic state
appears between the Haldane phase and period doubled N\'eel phase for the
integer spin chains. On the other hand, the transition from the
Tomonaga-Luttinger liquid state into the ferrimagnetic state takes place for
the half-odd-integer spin chains. In the ferrimagnetic phase, the spontaneous
magnetization varies continuously with the modulation amplitude of the single
site anisotropy. Eventually, the magnetization is locked to fractional values
of the saturated magnetization. These fractional values satisfy the
Oshikawa-Yamanaka-Affleck condition. The local spin profile is calculated to
reveal the physical nature of each state. In contrast to the case of
frustration induced ferrimagnetism, no incommensurate magnetic superstructure
is found.Comment: 5 pages, 7 figure
Hidden Order and Dimerization Transition in Chains
We study ground state properties of the quantum antiferromagnetic chain
with a bond alternation H = \sum_{j} [ 1 + \delta (-1)^j ] \mbox{\boldmath
$S$}_{j} \cdot \mbox{\boldmath $S$}_{j+1} by a Quantum Monte Carlo
calculation. We find that the hidden symmetry is broken for
while it is unbroken in the other regions. This confirms
the successive dimerization transitions first predicted by Affleck and Haldane.
Our result shows that these transitions can be understood in terms of the
hidden symmetry breaking, as was discussed using the
Valence-Bond-Solid states. Furthermore, we find that the behavior of the
generalized string correlation is qualitatively very similar to that in the
Valence-Bond-Solid states, including the location of zeroes as a function of
the angle parameter.Comment: 3 pages (LaTex with jpsj-style files
(ftp://ftp.u-tokyo.ac.jp/pub/SOCIETY/JPSJ)) and 1 Postscript figur
Density Matrix Renormalization Group Study of the Haldane Phase in Random One-Dimensional Antiferromagnets
It is conjectured that the Haldane phase of the S=1 antiferromagnetic
Heisenberg chain and the ferromagnetic-antiferromagnetic alternating
Heisenberg chain is stable against any strength of randomness, because of
imposed breakdown of translational symmetry. This conjecture is confirmed by
the density matrix renormalization group calculation of the string order
parameter and the energy gap distribution.Comment: 4 Pages, 7 figures; Considerable revisions are made in abstract and
main text. Final accepted versio
Disordered Flat Phase and Phase Diagram for Restricted Solid on Solid Models of Fcc(110) Surfaces
We discuss the results of a study of restricted solid-on-solid models for fcc
(110) surfaces. These models are simple modifications of the exactly solvable
BCSOS model, and are able to describe a missing-row reconstructed
surface as well as an unreconstructed surface. They are studied in two
different ways. The first is by mapping the problem onto a quantum spin-1/2
one-dimensional hamiltonian of the Heisenberg type, with competing
couplings. The second is by standard Monte Carlo simulations. We find phase
diagrams with the following features, which we believe to be quite generic: (i)
two flat, ordered phases (unreconstructed and missing-row reconstructed); a
rough, disordered phase; an intermediate disordered flat (DF) phase,
characterized by monoatomic steps, whose physics is shown to be akin to that of
a dimer spin state. (ii) a transition line from the reconstructed
phase to the DF phase showing exponents which appear to be close, within our
numerical accuracy, to the 2D-Ising universality class. (iii) a critical
(preroughening) line with variable exponents, separating the unreconstructed
phase from the DF phase. Possible signatures and order parameters of the DF
phase are investigated.Comment: Revtex (22 pages) + 15 figures (uuencoded file
Interacting Arrays of Steps and Lines in Random Media
The phase diagram of two interacting planar arrays of directed lines in
random media is obtained by a renormalization group analysis. The results are
discussed in the contexts of the roughening of reconstructed crystal surfaces,
and the pinning of flux line arrays in layered superconductors. Among the
findings are a glassy flat phase with disordered domain structures, a novel
second-order phase transition with continuously varying critical exponents, and
the generic disappearance of the glassy ``super-rough'' phases found previously
for a single array.Comment: 4 pages, REVTEX 3.0, uses epsf,multicol, 3 .eps-figures, submitted to
PR
Entanglement Entropy of One-dimensional Gapped Spin Chains
We investigate the entanglement entropy (EE) of gapped S=1 and spin
chains with dimerization. We find that the effective boundary degrees of
freedom as edge states contribute significantly to the EE. For the
dimerized Heisenberg chain, the EE of the sufficiently long chain is
essentially explained by the localized effective spins on the
boundaries. As for S=1, the effective spins are also causing a Kennedy
triplet that yields a lower bound for the EE. In this case, the residual
entanglement reduces substantially by a continuous deformation of the
Heisenberg model to that of the AKLT Hamiltonian.Comment: 5 pages, 6 figure
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