70 research outputs found
Effective numbers of charge carriers in doped graphene: The generalized Fermi liquid approach
The single-band current-dipole Kubo formula for the dynamical conductivity of
heavily doped graphene from Kup\v{c}i\'{c} [Phys. Rev. B 91, 205428 (2015)] is
extended to a two-band model for conduction electrons in lightly doped
graphene. Using a posteriori relaxation-time approximation in the two-band
quantum transport equations, with two different relaxation rates and one
quasi-particle lifetime, we explain a seemingly inconsistent dependence of the
dc conductivity of ultraclean and dirty
lightly doped graphene samples on electron doping, in a way consistent with the
charge continuity equation. It is also shown that the intraband contribution to
the effective number of conduction electrons in vanishes at K in the ultraclean regime, but it remains finite in
the dirty regime. The present model is shown to be consistent with a picture in
which the intraband and interband contributions to are characterized by two different mobilities of conduction electrons,
the values of which are well below the widely accepted value of mobility in
ultraclean graphene. The dispersions of Dirac and plasmon resonances are
reexamined to show that the present, relatively simple expression for the
dynamical conductivity tensor can be used to study simultaneously
single-particle excitations in the dc and optical conductivity and collective
excitations in energy loss spectroscopy experiments.Comment: 13 pages, 11 figure
Relativistic Energy Density Functional Description of Shape Transition in Superheavy Nuclei
Relativistic energy density functionals (REDF) provide a complete and
accurate, global description of nuclear structure phenomena. A modern
semi-empirical functional, adjusted to the nuclear matter equation of state and
to empirical masses of deformed nuclei, is applied to studies of shapes of
superheavy nuclei. The theoretical framework is tested in a comparison of
calculated masses, quadrupole deformations, and potential energy barriers to
available data on actinide isotopes. Self-consistent mean-field calculations
predict a variety of spherical, axial and triaxial shapes of long-lived
superheavy nuclei, and their alpha-decay energies and half-lives are compared
to data. A microscopic, REDF-based, quadrupole collective Hamiltonian model is
used to study the effect of explicit treatment of collective correlations in
the calculation of Q{\alpha} values and half-lives.Comment: 23 pages, 10 figure
New relativistic mean-field interaction with density-dependent meson-nucleon couplings
We adjust a new improved relativistic mean-field effective interaction with explicit density dependence of the meson-nucleon couplings. The effective interaction DD-ME2 is tested in relativistic Hartree-Bogoliubov and quasiparticle random-phase approximation (QRPA) calculations of nuclear ground states and properties of excited states, in calculation of masses, and it is applied to the analysis of very recent data on superheavy nuclei
Localization and clustering in the nuclear Fermi liquid
Using the framework of nuclear energy density functionals we examine the
conditions for single-nucleon localization and formation of cluster structures
in finite nuclei. We propose to characterize localization by the ratio of the
dispersion of single-nucleon wave functions to the average inter-nucleon
distance. This parameter generally increases with mass and describes the
gradual transition from a hybrid phase in light nuclei, characterized by the
spatial localization of individual nucleon states that leads to the formation
of cluster structures, toward the Fermi liquid phase in heavier nuclei. Values
of the localization parameter that correspond to a crystal phase cannot occur
in finite nuclei. Typical length and energy scales in nuclei allow the
formation of liquid drops, clusters, and halo structures.Comment: 6 pages, 3 figure
Constraints on the inner edge of neutron star crusts from relativistic nuclear energy density functionals
The transition density nt and pressure Pt at the inner edge between the liquid core and the solid crust of a neutron star are analyzed using the thermodynamical method and the framework of relativistic nuclear energy density functionals. Starting from a functional that has been carefully adjusted to experimental binding energies of finite nuclei, and varying the density dependence of the corresponding symmetry energy within the limits determined by isovector properties of finite nuclei, we estimate the constraints on the core-crust transition density and pressure of neutron stars: 0.086 fm-3⩽nt<0.090 fm-3 and 0.3 MeV fm-3
A microscopic estimate of the nuclear matter compressibility and symmetry energy in relativistic mean-field models
The relativistic mean-field plus RPA calculations, based on effective
Lagrangians with density-dependent meson-nucleon vertex functions, are employed
in a microscopic analysis of the nuclear matter compressibility and symmetry
energy. We compute the isoscalar monopole and the isovector dipole response of
Pb, as well as the differences between the neutron and proton radii for
Pb and several Sn isotopes. The comparison of the calculated excitation
energies with the experimental data on the giant monopole resonance in
Pb, restricts the nuclear matter compression modulus of structure
models based on the relativistic mean-field approximation to MeV. The isovector giant dipole resonance in Pb, and the
available data on differences between neutron and proton radii, limit the range
of the nuclear matter symmetry energy at saturation (volume asymmetry) to 32
MeV 36 MeV.Comment: 16 pages, 6 figure
Superallowed Fermi transitions in RPA with a relativistic point-coupling energy functional
The self-consistent random phase approximation (RPA) approach with the
residual interaction derived from a relativistic point-coupling energy
functional is applied to evaluate the isospin symmetry-breaking corrections
{\delta}c for the 0+\to0+ superallowed Fermi transitions. With these {\delta}c
values, together with the available experimental ft values and the improved
radiative corrections, the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM)
matrix is examined. Even with the consideration of uncertainty, the sum of
squared top-row elements has been shown to deviate from the unitarity condition
by 0.1% for all the employed relativistic energy functionals.Comment: 13 pages,2 figure
Microscopic analysis of nuclear quantum phase transitions in the N~90 region
The analysis of shape transitions in Nd isotopes, based on the framework of relativistic energy-density functionals and restricted to axially symmetric shapes in T. Nikšić, D. Vretenar, G. A. Lalazissis, and P. Ring [Phys. Rev. Lett. 99, 092502 (2007)], is extended to the region Z=60, 62, 64 with N[approximate]90 and includes both beta and gamma deformations. Collective excitation spectra and transition probabilities are calculated starting from a five-dimensional Hamiltonian for quadrupole vibrational and rotational degrees of freedom, with parameters determined by constrained self-consistent relativistic mean-field calculations for triaxial shapes. The results reproduce available data and show that there is an abrupt change of structure at N=90 that can be approximately characterized by the X(5) analytic solution at the critical point of the first-order quantum phase transition between spherical and axially deformed shapes
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