7,654 research outputs found
Algebraic Model for scattering of three-s-cluster systems. II. Resonances in the three-cluster continuum of 6He and 6Be
The resonance states embedded in the three-cluster continuum of 6He and 6Be
are obtained in the Algebraic Version of the Resonating Group Method. The model
accounts for a correct treatment of the Pauli principle. It also provides the
correct three-cluster continuum boundary conditions by using a Hyperspherical
Harmonics basis. The model reproduces the observed resonances well and achieves
good agreement with other models. A better understanding for the process of
formation and decay of the resonance states in six-nucleon systems is obtained.Comment: 8 pages, 10 postscript figures, submitted to Phys. Rev.
Suppression of 2D superconductivity by the magnetic field: quantum corrections vs superconductor-insulator transition
Magnetotransport of superconducting Nd_{2-x}Ce_xCuO_{4+y} (NdCeCuO) films is
studied in the temperature interval 0.3-30 K. The microscopic theory of the
quantum corrections to conductivity, both in the Cooper and in the diffusion
channels, qualitatively describes the main features of the experiment including
the negative magnetoresistance in the high field limit. Comparison with the
model of the field-induced superconductor-insulator transition (SIT) is
included and a crossover between these two theoretical approaches is discussed.Comment: 5 pages, 4 figures. Submitted to JETP Letter
Halo Excitation of He in Inelastic and Charge-Exchange Reactions
Four-body distorted wave theory appropriate for nucleon-nucleus reactions
leading to 3-body continuum excitations of two-neutron Borromean halo nuclei is
developed. The peculiarities of the halo bound state and 3-body continuum are
fully taken into account by using the method of hyperspherical harmonics. The
procedure is applied for A=6 test-bench nuclei; thus we report detailed studies
of inclusive cross sections for inelastic He(p,p')He and
charge-exchange Li(n,p)He reactions at nucleon energy 50 MeV. The
theoretical low-energy spectra exhibit two resonance-like structures. The first
(narrow) is the excitation of the well-known three-body resonance. The
second (broad) bump is a composition of overlapping soft modes of
multipolarities whose relative weights depend on
transferred momentum and reaction type. Inelastic scattering is the most
selective tool for studying the soft dipole excitation mode.Comment: Submitted to Phys. Rev. C., 11 figures using eps
Theoretical description of high-order harmonic generation in solids
We consider several aspects of high-order harmonic generation in solids: the
effects of elastic and inelastic scattering; varying pulse characteristics; and
inclusion of material-specific parameters through a realistic band structure.
We reproduce many observed characteristics of high harmonic generation
experiments in solids including the formation of only odd harmonics in
inversion-symmetric materials, and the nonlinear formation of high harmonics
with increasing field. We find that the harmonic spectra are fairly robust
against elastic and inelastic scattering. Furthermore, we find that the pulse
characteristics play an important role in determining the harmonic spectra.Comment: Accepted for publication in the New Journal of Physic
Cooper pair sizes in 11Li and in superfluid nuclei: a puzzle?
We point out a strong influence of the pairing force on the size of the two
neutron Cooper pair in Li, and to a lesser extent also in He. It
seems that these are quite unique situations, since Cooper pair sizes of stable
superfluid nuclei are very little influenced by the intensity of pairing, as
recently reported. We explore the difference between Li and heavier
superfulid nuclei, and discuss reasons for the exceptional situation in
Li.Comment: 9 pages. To be published in J. of Phys. G special issue on Open
Problems in Nuclear Structure (OPeNST
Breakup Reactions of 11Li within a Three-Body Model
We use a three-body model to investigate breakup reactions of 11Li (n+n+9Li)
on a light target. The interaction parameters are constrained by known
properties of the two-body subsystems, the 11Li binding energy and
fragmentation data. The remaining degrees of freedom are discussed. The
projectile-target interactions are described by phenomenological optical
potentials. The model predicts dependence on beam energy and target,
differences between longitudinal and transverse momentum distributions and
provides absolute values for all computed differential cross sections. We give
an almost complete series of observables and compare with corresponding
measurements. Remarkably good agreement is obtained. The relative neutron-9Li
p-wave content is about 40%. A p-resonance, consistent with measurements at
about 0.5 MeV of width about 0.4 MeV, seems to be necessary. The widths of the
momentum distributions are insensitive to target and beam energy with a
tendency to increase towards lower energies. The transverse momentum
distributions are broader than the longitudinal due to the diffraction process.
The absolute values of the cross sections follow the neutron-target cross
sections and increase strongly for beam energies decreasing below 100 MeV/u.Comment: 19 pages, 14 figures, RevTeX, psfig.st
Three-body Faddeev Calculation for 11Li with Separable Potentials
The halo nucleus Li is treated as a three-body system consisting of an
inert core of Li plus two valence neutrons. The Faddeev equations are
solved using separable potentials to describe the two-body interactions,
corresponding in the n-Li subsystem to a p resonance plus a
virtual s-wave state. The experimental Li energy is taken as input and
the Li transverse momentum distribution in Li is studied.Comment: 6 pages, RevTeX, 1 figur
Is the tetraneutron a bound dineutron-dineutron molecule?
In light of a new experiment which claims a positive identification, we
discuss the possible existence of the tetraneutron. We explore a novel model
based on a dineutron-dineutron molecule. We show that this model is not able to
explain the tetraneutron as a bound state, in agreement with other theoretical
models already discussed in the literature.Comment: 9 pages, 3 figures, J. Phys. G, in pres
Evidence for vortex staircases in the whole angular range due to competing correlated pinning mechanisms
We analyze the angular dependence of the irreversible magnetization of
YBaCuO crystals with columnar defects inclined from the c-axis. At
high fields a sharp maximum centered at the tracks' direction is observed. At
low fields we identify a lock-in phase characterized by an angle-independent
pinning strength and observe an angular shift of the peak towards the c-axis
that originates in the material anisotropy. The interplay among columnar
defects, twins and ab-planes generates a variety of staircase structures. We
show that correlated pinning dominates for all field orientations.Comment: 9 figures, 4 figure
Sensitivities of the Proton-Nucleus Elastical Scattering Observables of 6He and 8He at Intermediate Energies
We investigate the use of proton-nucleus elastic scattering experiments using
secondary beams of 6He and 8He to determine the physical structure of these
nuclei. The sensitivity of these experiments to nuclear structure is examined
by using four different nuclear structure models with different spatial
features using a full-folding optical potential model. The results show that
elastic scattering at intermediate energies (<100 MeV per nucleon) is not a
good constraint to be used to determine features of structure. Therefore
researchers should look elsewhere to put constraints on the ground state wave
function of the 6He and 8He nuclei.Comment: To be published in Phys. Rev.
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