509 research outputs found
Spin-Isospin Excitations and Muon Capture by Nuclei
By analyzing the energy-weighted moments of the strength function calculated
in RPA and beyond it is shown that the explanation of the effect of missing
strength of Gamow-Teller transitions requires that residual interaction produce
high-excited particle-hole collective states. The example of this
interaction is presented. The manifestations of spin-isospin nuclear response
in nuclear muon capture are discussed.Comment: 16 pages, 5 figures, 2 tables. The talk at the XVI International
School on Nuclear Physics, Neutron Physics and Nuclear Energy, September
19-26, Varna, Bulgari
Theoretical investigation of TbNi_{5-x}Cu_x optical properties
In this paper we present theoretical investigation of optical conductivity
for intermetallic TbNi_{5-x}Cu_x series. In the frame of LSDA+U calculations
electronic structure for x=0,1,2 and on top of that optical conductivities were
calculated. Disorder effects of Ni for Cu substitution on a level of LSDA+U
densities of states (DOS) were taken into account via averaging over all
possible Cu ion positions for given doping level x. Gradual suppression and
loosing of structure of optical conductivity at 2 eV together with simultaneous
intensity growth at 4 eV correspond to increase of Cu and decrease of Ni
content. As reported before [Knyazev et al., Optics and Spectroscopy 104, 360
(2008)] plasma frequency has non monotonic doping behaviour with maximum at
x=1. This behaviour is explained as competition between lowering of total
density of states on the Fermi level N(E_F) and growing of number of carriers.
Our theoretical results agree well with variety of recent experiments.Comment: 4 pages, 3 figure
Microscopic Calculation of Total Ordinary Muon Capture Rates for Medium - Weight and Heavy Nuclei
Total Ordinary Muon Capture (OMC) rates are calculated on the basis of the
Quasiparticle Random Phase Approximation for several spherical nuclei from
90^Zr to 208^Pb. It is shown that total OMC rates calculated with the free
value of the axial-vector coupling constant g_A agree well with the
experimental data for medium-size nuclei and exceed considerably the
experimental rates for heavy nuclei. The sensitivity of theoretical OMC rates
to the nuclear residual interactions is discussed.Comment: 27 pages and 3 figure
Optical spectroscopy and electronic structure of compounds HoNi 5-x Alx (x = 0, 1, 2)
The optical properties of the compounds HoNi5 - x Al x (x = 0, 1, 2) have been investigated using the ellipsometric method in the wavelength range from 0.22 to 16 μm. The electronic structure of these intermetallic compounds has been calculated in the local electron-spin density approximation with the correction for strong electronic interactions in the 4f shell of the holmium ions. The experimental dispersion dependences of optical conductivity in the region of interband light absorption have been interpreted based on the results of the calculation of the electron density of states. The plasma and relaxation frequencies of electrons have been determined. © 2013 Pleiades Publishing, Ltd
Optical spectroscopy and electronic structure of the GdCux compounds (x = 1, 2, 5)
Optical properties of the GdCu, GdCu2, and GdCu5 compounds with various crystal lattices have been investigated using ellipsometry in a spectral range of 0. 22-16 μm. Theoretical calculations of the electronic structure of these intermetallic compounds have been performed in the approximation of local electron density with the correction for strong electron correlations in a 4f shell of gadolinium ions. Based on the results of calculations, the interpretation of experimental spectra of interband optical conductivity has been proposed. The plasma and relaxation frequencies of conduction electrons have been determined. © 2013 Pleiades Publishing, Ltd
Influence of aluminum impurity on the electronic structure and optical properties of the TbNi5 intermetallic compound
The electronic structure of the TbNi5 - xAlx intermetallic compounds (x = 0, 1, 2) is calculated in the local electron density approximation with the correction to strong electron correlations in 4f shell of terbium ions. Spectral properties of these compounds are measured by ellipsometry in a wavelength range of 0. 22-16 μm. Frequency dependences of optical conductivity in the region of interband optical absorption are interpreted based on the results of calculations of electron densities of states. The relaxation and plasma frequencies of conduction electrons are determined. © 2013 Pleiades Publishing, Ltd
Specific features of the electronic structure and spectral properties of NdNi5 - xCux compounds
The spectral properties of the intermetallic compounds NdNi5 - xCux (x = 0, 1, 2) have been studied using optical ellipsometry in the wavelength range 0.22-16 μm. It has been established that substitution of copper atoms for nickel leads to noticeable changes in the optical absorption spectra, plasma frequencies, and relaxation frequencies of conduction electrons. Spin-polarized calculations of the electronic structure of these compounds have been performed in the local spin density approximation allowing for strong electron correlations (LSDA + U method) in the 4f shell of the rare-earth ion. The calculated electron densities of states have been used to interpret the experimental dispersion curves of optical conductivity in the interband light absorption region. © 2013 Pleiades Publishing, Ltd
One- and two-particle correlation functions in the cluster perturbation theory for cuprates
Physics of high- superconducting cuprates is obscured by the effect of
strong electronic correlations. One way to overcome the problem is to seek for
an exact solution at least within the small cluster and expand it to the whole
crystal. Such an approach is in the heart of the cluster perturbation theory
(CPT). Here we develop CPT for the dynamic spin and charge susceptibilities
(spin-CPT and charge-CPT), within which the correlation effects are explicitly
taken into account by the exact diagonalization. We apply spin-CPT and
charge-CPT to the effective two-band Hubbard model for the cuprates obtained
from the three-band Emery model and calculate one- and two-particle correlation
functions, namely, spectral function and spin and charge susceptibilities.
Doping dependence of the spin susceptibility was studied within spin-CPT and
CPT-RPA that is the CPT generalization of the random phase approximation (RPA).
Both methods produce the low energy response at four incommensurate wave
vectors in qualitative agreement to the results of the inelastic neutron
scattering on overdoped cuprates.Comment: 14 pages, 8 figure
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