1,266 research outputs found
Magnetic properties of cuprate perovskites in the normal state
Normal-state magnetic properties of cuprate high-T_c superconductors are
interpreted based on the self-consistent solution of the t-J model of Cu-O
planes. The solution method retains the rotation symmetry of spin components in
the paramagnetic state and has no preset magnetic ordering. The obtained
solution is homogeneous. The calculated temperature and concentration
dependencies of the magnetic susceptibility are close to those observed in
experiment. These results offer explanations for the observed scaling of the
static uniform susceptibility and for the changes in the spin correlation
length, spin-lattice and spin-echo decay rates in terms of the temperature and
doping variations in the spin excitation spectrum.Comment: 9 pages, 5 figure
17O NMR study of q=0 spin excitations in a nearly ideal S=1/2 1D Heisenberg antiferromagnet, Sr2CuO3, up to 800 K
We used 17O NMR to probe the uniform (wavevector q=0) electron spin
excitations up to 800 K in Sr2CuO3 and separate the q=0 from the q=\pm\pi/a
staggered components. Our results support the logarithmic decrease of the
uniform spin susceptibility below T ~ 0.015J, where J=2200 K. From measurement
of the dynamical spin susceptibility for q=0 by the spin-lattice relaxation
rate 1/T_{1}, we demonstrate that the q=0 mode of spin transport is ballistic
at the T=0 limit, but has a diffusion-like contribution at finite temperatures
even for T << J.Comment: Submitted to Phys. Rev. Lett. 4 pages, 4 figure
Probing anharmonic properties of nuclear surface vibration by heavy-ion fusion reactions
Describing fusion reactions between ^{16}O and ^{154}Dy and, between ^{16}O
and ^{144}Sm by the and interacting boson model, we show that
heavy-ion fusion reactions are strongly affected by anharmonic properties of
nuclear surface vibrations and nuclear shape, and thus provide a powerful
method to study details of nuclear structure and dynamics.Comment: 8 pages, 5 figures, To be published in the Proceedings of the FUSION
97 Conference, South Durras, Australia, March 1997 (J. Phys. G
Physics of cuprates with the two-band Hubbard model - The validity of the one-band Hubbard model
We calculate the properties of the two-band Hubbard model using the Dynamical
Cluster Approximation. The phase diagram resembles the generic phase diagram of
the cuprates, showing a strong asymmetry with respect to electron and hole
doped regimes, in agreement with experiment. Asymmetric features are also seen
in one-particle spectral functions and in the charge, spin and d-wave pairing
susceptibility functions. We address the possible reduction of the two-band
model to a low-energy single-band one, as it was suggested by Zhang and Rice.
Comparing the two-band Hubbard model properties with the single-band Hubbard
model ones, we have found similar low-energy physics provided that the
next-nearest-neighbor hopping term t' has a significant value (). The parameter t' is the main culprit for the electron-hole asymmetry.
However, a significant value of t' cannot be provided in a strict Zhang and
Rice picture where the extra holes added into the system bind to the existing
Cu holes forming local singlets. We notice that by considering approximate
singlet states, such as plaquette ones, reasonable values of t', which capture
qualitatively the physics of the two-band model can be obtained. We conclude
that a single-band t-t'-U Hubbard model captures the basic physics of the
cuprates concerning superconductivity, antiferromagnetism, pseudogap and
electron-hole asymmetry, but is not suitable for a quantitative analysis or to
describe physical properties involving energy scales larger than about 0.5 eV.Comment: 14 pages, 16 figure
Fusion barrier distributions in systems with finite excitation energy
Eigen-channel approach to heavy-ion fusion reactions is exact only when the
excitation energy of the intrinsic motion is zero. In order to take into
account effects of finite excitation energy, we introduce an energy dependence
to weight factors in the eigen-channel approximation. Using two channel
problem, we show that the weight factors are slowly changing functions of
incident energy. This suggests that the concept of the fusion barrier
distribution still holds to a good approximation even when the excitation
energy of the intrinsic motion is finite. A transition to the adiabatic
tunneling, where the coupling leads to a static potential renormalization, is
also discussed.Comment: 9 pages, 4 figures, Submitted to Physical Review
Radiation correction to astrophysical fusion reactions and the electron screening problem
We discuss the effect of electromagnetic environment on laboratory
measurements of the nuclear fusion reactions of astrophysical interest. The
radiation field is eliminated using the path integral formalism in order to
obtain the influence functional, which we evaluate in the semi-classical
approximation. We show that enhancement of the tunneling probability due to the
radiation correction is extremely small and does not resolve the longstanding
problem that the observed electron screening effect is significantly larger
than theoretical predictions.Comment: 9 pages, 1 eps figure
Addendum: Attenuation of the intensity within a superdeformed band
We investigate a random matrix model [Phys. Rev. C {\bf 65} 024302 (2002] for
the decay-out of a superdeformed band as a function of the parameters:
, , and . Here
is the spreading width for the mixing of an SD state
with a normally deformed (ND) doorway state , and
are the electromagnetic widths of the the SD and ND states respectively, is
the mean level spacing of the compound ND states and is the energy
difference between and . The maximum possible effect of an
order-chaos transition is inferred from analytical and numerical calculations
of the decay intensity in the limiting cases for which the ND states obey
Poisson and GOE statistics. Our results show that the sharp attenuation of the
decay intensity cannot be explained solely by an order-chaos transition.Comment: 4 pages, 4 figures, submitted to Physical Review
Phase separation versus supersolid behavior in frustrated antiferromagnets
We investigate the competition between spin-supersolidity and phase
separation in a frustrated spin-half model of weakly coupled dimers. We start
by considering systems of hard-core bosons on the square lattice, onto which
the low-energy physics of the herein investigated spin model can be mapped, and
devise a criterion for gauging the interplay between supersolid order and
domain wall formation based on strong coupling arguments. Effective bosonic
models for the spin model are derived via the contractor renormalization (CORE)
algorithm and we propose to combine a self-consistent cluster mean-field
solution with our criterion for the occurrence of phase separation to derive
the phase diagram as a function of frustration and magnetic field. In the limit
of strong frustration, the model is shown to be unstable toward phase
separation, in contradiction with recently published results. However, a region
of stable supersolidity is identified for intermediate frustration, in a
parameter range not investigated so far and of possible experimental relevance.Comment: 8 pages, 7 figures. Published versio
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