2,322 research outputs found
Structure of the doublet bands in doubly odd nuclei: The case of
The structure of the doublet bands in is
investigated within the framework of the Interacting Vector Boson Fermion Model
(IVBFM). A new, purely collective interpretation of these bands is given on the
basis of the used boson-fermion dynamical symmetry of the model. The energy
levels of the doublet bands as well as the absolute and
transition probabilities between the states of both yrast and yrare bands are
described quite well. The observed odd-even staggering of both and
values is reproduced by the introduction of an appropriate interaction
term of quadrupole type, which produces such a staggering effect in the
transition strengths. The calculations show that the appearance of doublet
bands in certain odd-odd nuclei could be a consequence of the realization of a
larger dynamical symmetry based on the non-compact supersymmetry group
.Comment: 12 pages, 8 figure
Collective excitations in the Unitary Correlation Operator Method and relativistic QRPA studies of exotic nuclei
The collective excitation phenomena in atomic nuclei are studied in two
different formulations of the Random Phase Approximation (RPA): (i) RPA based
on correlated realistic nucleon-nucleon interactions constructed within the
Unitary Correlation Operator Method (UCOM), and (ii) relativistic RPA (RRPA)
derived from effective Lagrangians with density-dependent meson-exchange
interactions. The former includes the dominant interaction-induced short-range
central and tensor correlations by means of an unitary transformation. It is
shown that UCOM-RPA correlations induced by collective nuclear vibrations
recover a part of the residual long-range correlations that are not explicitly
included in the UCOM Hartree-Fock ground state. Both RPA models are employed in
studies of the isoscalar monopole resonance (ISGMR) in closed-shell nuclei
across the nuclide chart, with an emphasis on the sensitivity of its properties
on the constraints for the range of the UCOM correlation functions. Within the
Relativistic Quasiparticle RPA (RQRPA) based on Relativistic Hartree-Bogoliubov
model, the occurrence of pronounced low-lying dipole excitations is predicted
in nuclei towards the proton drip-line. From the analysis of the transition
densities and the structure of the RQRPA amplitudes, it is shown that these
states correspond to the proton pygmy dipole resonance.Comment: 15 pages, 4 figures, submitted to Physics of Atomic Nuclei,
conference proceedings, "Frontiers in the Physics of Nucleus", St.
Petersburg, 28. June-1. July, 200
Bursts in the Chaotic Trajectory Lifetimes Preceding the Controlled Periodic Motion
The average lifetime () it takes for a randomly started trajectory
to land in a small region () on a chaotic attractor is studied. is
an important issue for controlling chaos. We point out that if the region
is visited by a short periodic orbit, the lifetime strongly deviates
from the inverse of the naturally invariant measure contained within that
region (). We introduce the formula that relates
to the expanding eigenvalue of the short periodic orbit
visiting .Comment: Accepted for publication in Phys. Rev. E, 3 PS figure
Incompressibility of finite fermionic systems: stable and exotic atomic nuclei
The incompressibility of finite fermionic systems is investigated using
analytical approaches and microscopic models. The incompressibility of a system
is directly linked to the zero-point kinetic energy of constituent fermions,
and this is a universal feature of fermionic systems. In the case of atomic
nuclei, this implies a constant value of the incompressibility in medium-heavy
and heavy nuclei. The evolution of nuclear incompressibility along Sn and Pb
isotopic chains is analyzed using global microscopic models, based on both
non-relativistic and relativistic energy functionals. The result is an almost
constant incompressibility in stable nuclei and systems not far from stability,
and a steep decrease in nuclei with pronounced neutron excess, caused by the
emergence of a soft monopole mode in neutron-rich nuclei.Comment: 7 pages, 5 figure
Transport, magnetic and superconducting properties of RuSr2RCu2O8 (R= Eu, Gd) doped with Sn
Ru{1-x}Sn{x}Sr2EuCu2O8 and Ru{1-x}Sn{x}Sr2GdCu2O8 have been comprehensively
studied by microwave and dc resistivity and magnetoresistivity and by the dc
Hall measurements. The magnetic ordering temperature T_m is considerably
reduced with increasing Sn content. However, doping with Sn leads to only
slight reduction of the superconducting critical temperature T_c accompanied
with the increase of the upper critical field B_c2, indicating an increased
disorder in the system and a reduced scattering length of the conducting holes
in CuO2 layers. In spite of the increased scattering rate, the normal state
resistivity and the Hall resistivity are reduced with respect to the pure
compound, due to the increased number of itinerant holes in CuO2 layers, which
represent the main conductivity channel. Most of the electrons in RuO2 layers
are presumably localized, but the observed negative magnetoresistance and the
extraordinary Hall effect lead to the conclusion that there exists a small
number of itinerant electrons in RuO layers that exhibit colossal
magnetoresistance.Comment: 10 pages, 9 figure
New Description of the Doublet Bands in Doubly Odd Nuclei
The experimentally observed doublet bands in some odd-odd
nuclei are analyzed within the orthosymplectic extension of the Interacting
Vector Boson Model (IVBM). A new, purely collective interpretation of these
bands is given on the basis of the obtained boson-fermion dynamical symmetry of
the model. It is illustrated by its application to three odd-odd nuclei from
the region, namely , and . The
theoretical predictions for the energy levels of the doublet bands as well as
and transition probabilities between the states of the yrast band in
the last two nuclei are compared with experiment and the results of other
theoretical approaches. The obtained results reveal the applicability of the
orthosymplectic extension of the IVBM.Comment: 15 pages, 13 figure
Nanoscale Electronic Order in Iron Pnictides
The charge distribution in RFeAs (R=La, Sm) iron pnictides is probed using As NQR. Whereas undoped and optimally-doped/overdoped compounds feature a single charge environment, two charge environments are detected in the underdoped region. Spin- lattice relaxation measurements show their coexistence at the nanoscale. Together with the quantitative variations of the spectra with doping, they point at a local electronic order in the iron layers, where low- and high-doping-like regions would coexist. Implications for the interplay of static magnetism and superconductivity are discussed
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Electronic properties of LaO1-xFxFeAs in the normal state probed by nmr/nqr
We report 139La, 57Fe and 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on powders of the new LaO1−xFxFeAs superconductor for x=0 and 0.1 at temperatures up to 480 K, and compare our measured NQR spectra with local density approximation (LDA) calculations. For all three nuclei in the x=0.1 material, it is found that the local Knight shift increases monotonically with an increase in temperature, and scales with the macroscopic susceptibility, suggesting a single magnetic degree of freedom. Surprisingly, the spin lattice relaxation rates for all nuclei also scale with one another, despite the fact that the form factors for each site sample different regions of q-space. This result suggests a lack of any q-space structure in the dynamical spin susceptibility that might be expected in the presence of antiferromagnetic correlations. Rather, our results are more compatible with simple quasi-particle scattering. Furthermore, we find that the increase in the electric field gradient at the As cannot be accounted for by LDA calculations, suggesting that structural changes, in particular the position of the As in the unit cell, dominate the NQR response
Misleading signatures of quantum chaos
The main signature of chaos in a quantum system is provided by spectral
statistical analysis of the nearest neighbor spacing distribution and the
spectral rigidity given by . It is shown that some standard
unfolding procedures, like local unfolding and Gaussian broadening, lead to a
spurious increase of the spectral rigidity that spoils the
relationship with the regular or chaotic motion of the system. This effect can
also be misinterpreted as Berry's saturation.Comment: 4 pages, 5 figures, submitted to Physical Review
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