864 research outputs found
Charge Dynamics from Copper Oxide Materials
The charge dynamics of the copper oxide materials in the underdoped and
optimal doped regimes is studied within the framework of the fermion-spin
theory. The conductivity spectrum shows the non-Drude behavior at low energies
and unusual midinfrared peak, and the resistivity exhibits a linear behavior in
the temperature, which are consistent with experiments and numerical
simulations.Comment: 10 pages, the figures are not included and can be air-mailed by
reques
Optical and transport properties in doped two-leg ladder antiferromagnet
Within the t-J model, the optical and transport properties of the doped
two-leg ladder antiferromagnet are studied based on the fermion-spin theory. It
is shown that the optical and transport properties of the doped two-leg ladder
antiferromagnet are mainly governed by the holon scattering. The low energy
peak in the optical conductivity is located at a finite energy, while the
resistivity exhibits a crossover from the high temperature metallic-like
behavior to the low temperature insulating-like behavior, which are consistent
with the experiments.Comment: 13 pages, 5 figures, accepted for publication in Phys. Rev. B65
(2002) (April 15 issue
Coexistence of the Electron Cooper Pair and Antiferromagnetic Short-Range Correlation in Copper Oxide Materials
Within the fermion-spin theory, the physical properties of the electron
pairing state in the copper oxide materials are discussed. According to the
common form of the electron Cooper pair, it is shown that there is a
coexistence of the electron Cooper pair and magnetic short-range correlation,
and hence the antiferromagnetic short-range correlation can persist into the
superconducting state. Moreover, the mean-field results indicate that the
electron pairing state originating from the pure magnetic interaction in the
two-dimensional t-J model is the local state, and then does not reveal the true
superconducting ground-state.Comment: 6 pages, Revtex, Four figures are adde
A novel and simple spectral method for nonlocal PDEs with the fractional Laplacian
We propose a novel and simple spectral method based on the semi-discrete
Fourier transforms to discretize the fractional Laplacian
. Numerical analysis and experiments are provided
to study its performance. Our method has the same symbol as the
fractional Laplacian at the discrete level, and
thus it can be viewed as the exact discrete analogue of the fractional
Laplacian. This {\it unique feature} distinguishes our method from other
existing methods for the fractional Laplacian. Note that our method is
different from the Fourier pseudospectral methods in the literature, which are
usually limited to periodic boundary conditions (see Remark \ref{remark0}).
Numerical analysis shows that our method can achieve a spectral accuracy. The
stability and convergence of our method in solving the fractional Poisson
equations were analyzed. Our scheme yields a multilevel Toeplitz stiffness
matrix, and thus fast algorithms can be developed for efficient matrix-vector
products. The computational complexity is , and the
memory storage is with the total number of points.
Extensive numerical experiments verify our analytical results and demonstrate
the effectiveness of our method in solving various problems
Disorder effects on the quantum coherence of a many-boson system
The effects of disorders on the quantum coherence for many-bosons are studied
in a double well model. For the ground state, the disorder enhances the quantum
coherence. In the deep Mott regime, dynamical evolution reveals periodical
collapses and revivals of the quantum coherence which is robust against the
disorder. The average over variations in both the on-site energy and the
interaction reveals a beat phenomenon of the coherence-decoherence oscillation
in the temporal evolution.Comment: 4 figure
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