1,274 research outputs found
Anharmonic phonon excitations in subbarrier fusion reactions
Recently measured high precision data of fusion excitation function have
enabled a detailed study on the effects of nuclear collective excitations on
fusion reactions. Using such highly accurate data of the O +
Sm reactions, we discuss the anharmonic properties of collective
phonon excitations in Sm nuclei. It is shown that subbarrier fusion
reactions are strongly affected by the anharmonic effects and thus offer an
alternative method to extract the static quadrupole moments of phonon states in
a spherical nucleus.Comment: 10 pages, To be published in the Proceedings of the Tours Symposium
on Nuclear Physics III, Tours, France, September 1997 (American Institute of
Physics
Possible Localized Modes in the Uniform Quantum Heisenberg Chains of Sr2CuO3
A model of mobile-bond defects is tentatively proposed to analyze the
"anomalies" observed on the NMR spectrum of the quantum Heisenberg chains of
Sr2CuO3. A bond-defect is a local change in the exchange coupling. It results
in a local alternating magnetization (LAM), which when the defect moves,
creates a flipping process of the local field seen by each nuclear spin. At low
temperature, when the overlap of the LAM becomes large, the defects form a
periodic structure, which extends over almost all the chains. In that regime,
the density of bond-defects decreases linearly with T.Comment: 4 pages + 3 figures. To appear in Physical Review
NMR evidence for the persistence of spin-superlattice above the 1/8 magnetization plateau in SrCu2(BO3)2
We present 11B NMR studies of the 2D frustrated dimer spin system SrCu2(BO3)2
in the field range 27-31 T covering the upper phase boundary of the 1/8
magnetization plateau, identified at 28.4 T. Our data provide a clear evidence
that above 28.4 T the spin-superlattice of the 1/8 plateau is modified but does
not melt even though the magnetization increases. Although this is precisely
what is expected for a supersolid phase, the microscopic nature of this new
phase is much more complex. We discuss the field-temperature phase diagram on
the basis of our NMR data.Comment: 5 pages, 4 figures, published versio
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
Energy averages over regular and chaotic states in the decay out of superdeformed bands
We describe the decay out of a superdeformed band using the methods of
reaction theory. Assuming that decay-out occurs due to equal coupling (on
average) to a sea of equivalent chaotic normally deformed (ND) states, we
calculate the average intraband decay intensity and show that it can be written
as an ``optical'' background term plus a fluctuation term, in total analogy
with average nuclear cross sections. We also calculate the variance in closed
form. We investigate how these objects are modified when the decay to the ND
states occurs via an ND doorway and the ND states' statistical properties are
changed from chaotic to regular. We show that the average decay intensity
depends on two dimensionless variables in the first case while in the second
case, four variables enter the picture.Comment: 8 pages, 1 figure, presented at FUSION03, Matsushima, Miyagi, Japan,
Nov 12-15, 2003, to appear in Progress of Theoretical Physics; corrected
typo
Enhanced low-energy spin dynamics with diffusive character in the iron-based superconductor (La0.87Ca0.13)FePO: Analogy with high Tc cuprates (A short note)
In a recent NMR investigation of the iron-based superconductor
(La0.87Ca0.13)FePO [Phys. Rev. Lett. 101, 077006 (2008)] Y. Nakai et al.
reported an anomalous behavior of the nuclear spin-lattice relaxation of 31P
nuclei in the superconducting state: The relaxation rate 1/T1 strongly depends
on the measurement frequency and its T dependence does not show the typical
decrease expected for the superconducting state. In this short note, we point
out that these two observations bear similarity with the situation is some of
the high Tc cuprates.Comment: To appear in J. Phys. Soc. Jpn. (Short Note
Field Dependence of Electronic Specific Heat in Two-Band Superconductors
The vortex structure is studied in light of MgB theoretically based on a
two-band superconducting model by means of Bogoliubov-de Gennes framework. The
field dependence of the electronic specific heat coefficient is
focused. The exponent in is shown to
become smaller by adjusting the gap ratio of the two gaps on the major and
minor bands. The observed extremely small value could be
explained reasonably well in this two-band model with the gap ratio .Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jp
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
- âŠ