783 research outputs found
Making High T Higher: A Theoretical Proposal
There is considerable evidence that the highest obtainable in a
copper-oxide plane is limitted by the competition between two effects: On the
one hand, as the concentration of doped-holes, , is increased, the pairing
scale, which is related to the properties of a doped Mott insulator, decreases.
On the otherhand, the superfluid density, which controls the stiffness of the
system to phase fluctuations, vanishes as , and increases with
increasing . Optimal is obtained at a crossover from a phase ordering
dominated regime at small to a pairing dominated regime at large . If
this description is valid, then higher 's can be obtained in an array of
coupled planes with different doped hole concentrations, such that a high
pairing scale is derived from the underdoped planes and a large phase stiffness
from the optimally or overdoped ones.Comment: 6 page
Distribution of spectral weight in a system with disordered stripes
The ``band-structure'' of a disordered stripe array is computed and compared,
at a qualitative level, to angle resolved photoemission experiments on the
cuprate high temperature superconductors. The low-energy states are found to be
strongly localized transverse to the stripe direction, so the electron dynamics
is strictly one-dimensional (along the stripe). Despite this, aspects of the
two dimensional band-structure Fermi surface are still vividly apparent.Comment: 10 pages, 11 figure
Novel NN interaction and the spectroscopy of light nuclei
Nucleon-nucleon (NN) phase shifts and the spectroscopy of nuclei
are successfully described by an inverse scattering potential that is separable
with oscillator form factors.Comment: 4 pages, 1 figure, 13 table
The three-nucleon bound state using realistic potential models
The bound states of H and He have been calculated using the Argonne
plus the Urbana three-nucleon potential. The isospin state
have been included in the calculations as well as the - mass difference.
The H-He mass difference has been evaluated through the charge
dependent terms explicitly included in the two-body potential. The calculations
have been performed using two different methods: the solution of the Faddeev
equations in momentum space and the expansion on the correlated hyperspherical
harmonic basis. The results are in agreement within 0.1% and can be used as
benchmark tests. Results for the CD-Bonn interaction are also presented. It is
shown that the H and He binding energy difference can be predicted
model independently.Comment: 5 pages REVTeX 4, 1 figures, 6 table
Precision neutron interferometric measurements of the n-p, n-d, and n-3He zero-energy coherent neutron scattering amplitudes
We have performed high precision measurements of the zero-energy neutron
scattering amplitudes of gas phase molecular hydrogen, deuterium, and He
using neutron interferometry. We find
fm\cite{Schoen03},
fm\cite{Black03,Schoen03}, and
fm\cite{Huffman04}. When combined with the previous world data, properly
corrected for small multiple scattering, radiative corrections, and local field
effects from the theory of neutron optics and combined by the prescriptions of
the Particle Data Group, the zero-energy scattering amplitudes are:
fm, fm, and fm. The precision of
these measurements is now high enough to severely constrain NN few-body models.
The n-d and n-He coherent neutron scattering amplitudes are both now in
disagreement with the best current theories. The new values can be used as
input for precision calculations of few body processes. This precision data is
sensitive to small effects such as nuclear three-body forces, charge-symmetry
breaking in the strong interaction, and residual electromagnetic effects not
yet fully included in current models.Comment: 6 pages, 4 figures, submitted to Physica B as part of the Festschrift
honouring Samuel A. Werner at the International Conference on Neutron
Scattering 200
Three-Nucleon Force Effects in Nucleon Induced Deuteron Breakup: Predictions of Current Models (I)
An extensive study of three-nucleon force effects in the entire phase space
of the nucleon-deuteron breakup process, for energies from above the deuteron
breakup threshold up to 200 MeV, has been performed. 3N Faddeev equations have
been solved rigorously using the modern high precision nucleon-nucleon
potentials AV18, CD Bonn, Nijm I, II and Nijm 93, and also adding 3N forces. We
compare predictions for cross sections and various polarization observables
when NN forces are used alone or when the two pion-exchange Tucson-Melbourne
3NF was combined with each of them. In addition AV18 was combined with the
Urbana IX 3NF and CD Bonn with the TM' 3NF, which is a modified version of the
TM 3NF, more consistent with chiral symmetry. Large but generally model
dependent 3NF effects have been found in certain breakup configurations,
especially at the higher energies, both for cross sections and spin
observables. These results demonstrate the usefulness of the kinematically
complete breakup reaction in testing the proper structure of 3N forces.Comment: 42 pages, 20 ps figures, 2 gif figure
Highly optimized tolerance in epidemic models incorporating local optimization and regrowth
The Second Sound of SU(2)
Using the AdS/CFT correspondence, we calculate the transport coefficients of
a strongly interacting system with a non-abelian SU(2) global symmetry near a
second order phase transition. From the behavior of the poles in the Green's
functions near the phase transition, we determine analytically the speed of
second sound, the conductivity, and diffusion constants. We discuss
similarities and differences between this and other systems with vector order
parameters such as p-wave superconductors and liquid helium-3.Comment: 31 pages, 2 figures; v2 ref added, typo fixe
Interacting Electrons on a Fluctuating String
We consider the problem of interacting electrons constrained to move on a
fluctuating one-dimensional string. An effective low-energy theory for the
electrons is derived by integrating out the string degrees of freedom to lowest
order in the inverse of the string tension and mass density, which are assumed
to be large. We obtain expressions for the tunneling density of states, the
spectral function and the optical conductivity of the system. Possible
connections with the phenomenology of the cuprate high temperature
superconductors are discussed.Comment: 14 pages, 1 figur
Phase diagram of an Ising model with long-range frustrating interactions: a theoretical analysis
We present a theoretical study of the phase diagram of a frustrated Ising
model with nearest-neighbor ferromagnetic interactions and long-range
(Coulombic) antiferromagnetic interactions. For nonzero frustration, long-range
ferromagnetic order is forbidden, and the ground-state of the system consists
of phases characterized by periodically modulated structures. At finite
temperatures, the phase diagram is calculated within the mean-field
approximation. Below the transition line that separates the disordered and the
ordered phases, the frustration-temperature phase diagram displays an infinite
number of ``flowers'', each flower being made by an infinite number of
modulated phases generated by structure combination branching processes. The
specificities introduced by the long-range nature of the frustrating
interaction and the limitation of the mean-field approach are finally
discussed.Comment: 32 pages, 7 figure
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