3,677 research outputs found
Resonant magnetic mode in superconducting 2-leg ladders
The spin dynamics of a doped 2-leg spin ladder is investigated by numerical
techniques. We show that a hole pair-magnon boundstate evolves at finite hole
doping into a sharp magnetic excitation below the two-particle continuum. This
is supported by a field theory argument based on a SO(6)-symmetric ladder.
Similarities and differences with the resonant mode of the high-T cuprates
are discussed.Comment: 5 pages, 5 figure
Spatial and temporal filtering of a 10-W Nd:YAG laser with a Fabry-Perot ring-cavity premode cleaner
We report on the use of a fixed-spacer FabryâPerot ring cavity to filter spatially and temporally a 10-W laser-diode-pumped Nd:YAG master-oscillator power amplifier. The spatial filtering leads to a 7.6-W TEMinfinity beam with 0.1% higher-order transverse mode content. The temporal filtering reduces the relative power fluctuations at 10 MHz to 2.8 x 10^-/sqrtHz, which is 1 dB above the shot-noise limit for 50 mA of detected photocurrent
Perturbative dynamics of matrix string for the membrane
Recently Sekino and Yoneya proposed a way to regularize the world volume
theory of membranes wrapped around by matrices and showed that one
obtains matrix string theory as a regularization of such a theory. We show that
this correspondence between matrix string theory and wrapped membranes can be
obtained by using the usual M(atrix) theory techniques. Using this
correspondence, we construct the super-Poincare generators of matrix string
theory at the leading order in the perturbation theory. It is shown that these
generators satisfy 10 dimensional super-Poincar\'e algebra without any anomaly.Comment: 23 pages, 1 figur
A comparison study of regional atmospheric simulations with an elastic backscattering Lidar and sunphotometry in an urban area
We describe a comparison study of Aerosol Optical Thickness (AOT) from numerical simulations using a regional atmospheric model with an elastic backscattering lidar operating at 532 nm and a sunphotometer belonging to the AERONET network at SĂŁo Paulo (23° S 46° W) city, Brazil, a very populated urban area. The atmospheric model includes an aerosol emission, transport and deposition module coupled to a radiative transfer parameterization, which takes the interaction between aerosol particles and short and long wave radiation into account. A period of one week was taken as case study during the dry season (late August) when intense biomass burning activities occur at remote areas in South America, and meteorological conditions disfavor the pollution dispersion in the city of SĂŁo Paulo. The situation presented here showed how smoke from biomass burning in remote areas is transported to the south-east part of Brazil and affects the optical atmospheric conditions in SĂŁo Paulo. The numerical simulations are corroborated by in situ measurements of AOT obtained by lidar and sun photometry
A critical-density closed Universe in Brans-Dicke theory
In a Brans-Dicke (BD) cosmological model, the energy density associated with
some scalar field decreases as \displaystyle a^{{-2}(\frac{\omega_{o}+
{\frac12}%}{\omega_{o}+1})} with the scale factor of the Universe,
giving a matter with an Equation of state . In this model, the Universe
could be closed but still have a nonrelativistic-matter density corresponding
to its critical value, . Different cosmological expressions, such
as, luminosity distance, angular diameter, number count and ratio of the
redshift tickness-angular size, are determined in terms of the redshift for
this model.Comment: To appear in MNRAS, 7 pages, 5 eps figure
Elasticity-driven Nanoscale Texturing in Complex Electronic Materials
Finescale probes of many complex electronic materials have revealed a
non-uniform nanoworld of sign-varying textures in strain, charge and
magnetization, forming meandering ribbons, stripe segments or droplets. We
introduce and simulate a Ginzburg-Landau model for a structural transition,
with strains coupling to charge and magnetization. Charge doping acts as a
local stress that deforms surrounding unit cells without generating defects.
This seemingly innocuous constraint of elastic `compatibility', in fact induces
crucial anisotropic long-range forces of unit-cell discrete symmetry, that
interweave opposite-sign competing strains to produce polaronic elasto-magnetic
textures in the composite variables. Simulations with random local doping below
the solid-solid transformation temperature reveal rich multiscale texturing
from induced elastic fields: nanoscale phase separation, mesoscale intrinsic
inhomogeneities, textural cross-coupling to external stress and magnetic field,
and temperature-dependent percolation. We describe how this composite textured
polaron concept can be valuable for doped manganites, cuprates and other
complex electronic materials.Comment: Preprin
A Plaquette Basis for the Study of Heisenberg Ladders
We employ a plaquette basis-generated by coupling the four spins in a
lattice to a well-defined total angular momentum-for the study of
Heisenberg ladders with antiferromagnetic coupling. Matrix elements of the
Hamiltonian in this basis are evaluated using standard techniques in
angular-momentum (Racah) algebra. We show by exact diagonalization of small
( and ) systems that in excess of 90% of the ground-state
probability is contained in a very small number of basis states. These few
basis states can be used to define a severely truncated basis which we use to
approximate low-lying exact eigenstates. We show how, in this low-energy basis,
the isotropic spin-1/2 Heisenberg ladder can be mapped onto an anisotropic
spin-1 ladder for which the coupling along the rungs is much stronger than the
coupling between the rungs. The mapping thereby generates two distinct energy
scales which greatly facilitates understanding the dynamics of the original
spin-1/2 ladder. Moreover, we use these insights to define an effective
low-energy Hamiltonian in accordance to the newly developed COntractor
REnormalization group (CORE) method. We show how a simple range-2 CORE
approximation to the effective Hamiltonian to be used with our truncated basis
reproduces the low-energy spectrum of the exact theory at the \alt
1% level.Comment: 12 pages with two postscript figure
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