250 research outputs found
Dynamic nonlinear (cubic) susceptibility in quantum Ising spin glass
Dynamic nonlinear (cubic) susceptibility in quantum d-dimensional Ising spin
glass with short-range interactions is investigated on the basis of quantum
droplet model and quantum-mechanical nonlinear response theory. Nonlinear
response depends on the tunneling rate for a droplet which regulates the
strength of quantum fluctuations. It shows a strong dependence on the
distribution of droplet free energies and on the droplet length scale average.
Comparison with recent experiments on quantum spin glasses like disordered
dipolar quantum Ising magnet is discussed.Comment: 15 pages, 3 figure
Quantum vortex fluctuations in cuprate superconductors
We study the effects of quantum vortex fluctuations in two-dimensional
superconductors using a dual theory of vortices, and investigate the relevance
to underdoped cuprates where the superconductor-insulator transition (SIT) is
possibly driven by quantum vortex proliferation. We find that a broad enough
phase fluctuation regime may exist for experimental observation of the quantum
vortex fluctuations near SIT in underdoped cuprates. We propose that this
scenario can be tested via pair-tunneling experiments which measure the
characteristic resonances in the zero-temperature pair-field susceptibility in
the vortex-proliferated insulating phase.Comment: RevTex 5 pages, 2 eps figures; expanded; to appear in Phys. Rev.
Tensionless structure of glassy phase
We study a class of homogeneous finite-dimensional Ising models which were
recently shown to exhibit glassy properties. Monte Carlo simulations of a
particular three-dimensional model in this class show that the glassy phase
obtained under slow cooling is dominated by large scale excitations whose
energy scales with their size as with
. Simulations suggest that in another model of this class,
namely the four-spin model, energy is concentrated mainly in linear defects
making also in this case domain walls tensionless. Two-dimensinal variants of
these models are trivial and energy of excitations scales with the exponent
.Comment: 5 page
Phase Transitions in One-Dimensional Truncated Bosonic Hubbard Model and Its Spin-1 Analog
We study one-dimensional truncated (no more than 2 particles on a site)
bosonic Hubbard model in both repulsive and attractive regimes by exact
diagonalization and exact worldline Monte Carlo simulation. In the commensurate
case (one particle per site) we demonstrate that the point of Mott-insulator --
superfluid transition, , is remarkably far from that of
the full model. In the attractive region we observe the phase transition from
one-particle superfluid to two-particle one. The paring gap demonstrates a
linear behavior in the vicinity of the critical point. The critical state
features marginal response to the gauge phase. We argue that the two-particle
superfluid is a macroscopic analog of a peculiar phase observed earlier in a
spin-1 model with axial anisotropy.Comment: Revtex, 5 pages, 9 figures. Submitted to Phys. Rev.
Velocity-force characteristics of an interface driven through a periodic potential
We study the creep dynamics of a two-dimensional interface driven through a
periodic potential using dynamical renormalization group methods. We find that
the nature of weak-drive transport depends qualitatively on whether the
temperature is above or below the equilibrium roughening transition
temperature . Above , the velocity-force characteristics is Ohmic,
with linear mobility exhibiting a jump discontinuity across the transition. For
, the transport is highly nonlinear, exhibiting an interesting
crossover in temperature and weak external force . For intermediate drive,
, we find near a power-law velocity-force characteristics
, with , and well-below ,
, with . In the limit
of vanishing drive () the velocity-force characteristics crosses over
to , and is controlled by soliton nucleation.Comment: 18 pages, submitted to Phys. Rev.
Ultracold Atoms in 1D Optical Lattices: Mean Field, Quantum Field, Computation, and Soliton Formation
In this work, we highlight the correspondence between two descriptions of a
system of ultracold bosons in a one-dimensional optical lattice potential: (1)
the discrete nonlinear Schr\"{o}dinger equation, a discrete mean-field theory,
and (2) the Bose-Hubbard Hamiltonian, a discrete quantum-field theory. The
former is recovered from the latter in the limit of a product of local coherent
states. Using a truncated form of these mean-field states as initial
conditions, we build quantum analogs to the dark soliton solutions of the
discrete nonlinear Schr\"{o}dinger equation and investigate their dynamical
properties in the Bose-Hubbard Hamiltonian. We also discuss specifics of the
numerical methods employed for both our mean-field and quantum calculations,
where in the latter case we use the time-evolving block decimation algorithm
due to Vidal.Comment: 14 pages, 2 figures; to appear in Journal of Mathematics and
Computers in Simulatio
The one-dimensional Bose-Hubbard Model with nearest-neighbor interaction
We study the one-dimensional Bose-Hubbard model using the Density-Matrix
Renormalization Group (DMRG).For the cases of on-site interactions and
additional nearest-neighbor interactions the phase boundaries of the
Mott-insulators and charge density wave phases are determined. We find a direct
phase transition between the charge density wave phase and the superfluid
phase, and no supersolid or normal phases. In the presence of nearest-neighbor
interaction the charge density wave phase is completely surrounded by a region
in which the effective interactions in the superfluid phase are repulsive. It
is known from Luttinger liquid theory that a single impurity causes the system
to be insulating if the effective interactions are repulsive, and that an even
bigger region of the superfluid phase is driven into a Bose-glass phase by any
finite quenched disorder. We determine the boundaries of both regions in the
phase diagram. The ac-conductivity in the superfluid phase in the attractive
and the repulsive region is calculated, and a big superfluid stiffness is found
in the attractive as well as the repulsive region.Comment: 19 pages, 30 figure
Slow dynamics and aging in spin-glasses
Contribution presented by Eric Vincent in the Conference `Complex Behaviour
of Glassy Systems', Sitges, Barcelona, Spain, June, 1996. It contains a review
of the experimental results on Slow dynamics and aging in spin-glasses. It also
presents their comparison with recent theoretical developments in the
description of the out of equilibrium dynamics of disordered systems; namely,
the trap model and the mean-field theory.Comment: 35 pages, 12 figures, macro lmamult.sty (included
Using the Wigner-Ibach Surmise to Analyze Terrace-Width Distributions: History, User's Guide, and Advances
A history is given of the applications of the simple expression generalized
from the surmise by Wigner and also by Ibach to extract the strength of the
interaction between steps on a vicinal surface, via the terrace width
distribution (TWD). A concise guide for use with experiments and a summary of
some recent extensions are provided.Comment: 11 pages, 4 figures, reformatted (with revtex) version of refereed
paper for special issue of Applied Physics A entitled "From Surface Science
to Device Physics", in honor of the retirements of Prof. H. Ibach and Prof.
H. L\"ut
Phosphorothioate antisense oligonucleotides induce the formation of nuclear bodies
Antisense oligonucleotides are powerful tools for the in vivo regulation of gene expression. We have characterized the intracellular distribution of fluorescently tagged phosphorothioate oligodeoxynucleotides (PS-ONs) at high resolution under conditions in which PS-ONs have the potential to display antisense activity. Under these conditions PS-ONs predominantly localized to the cell nucleus where they accumulated in 20-30 bright spherical foci designated phosphorothioate bodies (PS bodies), which were set against a diffuse nucleoplasmic population excluding nucleoli. PS bodies are nuclear structures that formed in cells after PS-ON delivery by transfection agents or microinjection but were observed irrespectively of antisense activity or sequence. Ultrastructurally, PS bodies corresponded to electron-dense structures of 150-300 nm diameter and resembled nuclear bodies that were found with lower frequency in cells lacking PS-ONs. The environment of a living cell was required for the de novo formation of PS bodies, which occurred within minutes after the introduction of PS-ONs. PS bodies were stable entities that underwent noticeable reorganization only during mitosis. Upon exit from mitosis, PS bodies were assembled de novo from diffuse PS-ON pools in the daughter nuclei. In situ fractionation demonstrated an association of PS-ONs with the nuclear matrix. Taken together, our data provide evidence for the formation of a nuclear body in cells after introduction of phosphorothioate oligodeoxynucleotides
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