710 research outputs found
Knight Shift and Leading Superconducting Instability From Spin Fluctuations in Sr2RuO4
Recent nuclear magnetic resonance studies [A. Pustogow {\it et al.},
arXiv:1904.00047] have challenged the prevalent chiral triplet pairing scenario
proposed for SrRuO. To provide guidance from microscopic theory as to
which other pair states might be compatible with the new data, we perform a
detailed theoretical study of spin-fluctuation mediated pairing for this
compound. We map out the phase diagram as a function of spin-orbit coupling,
interaction parameters, and band-structure properties over physically
reasonable ranges, comparing when possible with photoemission and inelastic
neutron scattering data information. We find that even-parity pseudospin
singlet solutions dominate large regions of the phase diagram, but in certain
regimes spin-orbit coupling favors a near-nodal odd-parity triplet
superconducting state, which is either helical or chiral depending on the
proximity of the band to the van Hove points. A surprising
near-degeneracy of the nodal - and -wave solutions leads
to the possibility of a near-nodal time-reversal symmetry broken
pair state. Predictions for the temperature dependence
of the Knight shift for fields in and out of plane are presented for all
states.Comment: 5 pages (3 figures) + supplementary informatio
Eliashberg theory of superconductivity and inelastic rare-earth impurity scattering in filled skutterudite LaPrOsSb
We study the influence of inelastic rare-earth impurity scattering on
electron-phonon mediated superconductivity and mass renormalization in
(LaPr)OsSb compounds. Solving the strong coupling
Eliashberg equations we find that the dominant quadrupolar component of the
inelastic scattering on Pr impurities yields an enhancement of the
superconducting transition temperature T in LaOsSb and
increases monotonically as a function of Pr concentration. The calculated
results are in good agreement with the experimentally observed T
dependence. Our analysis suggests that phonons and quadrupolar excitations
cause the attractive electron interaction which results in the formation of
Cooper pairs and singlet superconductivity in PrOsSb.Comment: 5 pages,4 figures, revised title suggested by editor, original fig.4
and fig.5 combined together, discussion added before conclusio
Dynamical charge susceptibility in layered cuprates: the influence of screened inter-site Coulomb repulsion
The analytical expression for dynamical charge susceptibility in layered
cuprates has been derived in the frame of singlet-correlated band model beyond
random-phase-approximation (RPA) scheme. Our calculations performed near
optimal doping regime show that there is a peak in real part of the charge
susceptibility at {\bf Q} = (, ) at strong
enough inter-site Coulomb repulsion. Together with the strong maximum in the Im
at 15 meV it confirms the formation of low-energetic
plasmons or charge fluctuations. This provides a jsutification that these
excitations are important and together with a spin flcutuations can contribute
to the Cooper pairing in layered cuprates. Analysing the charge susceptibilitiy
with respect to an instability we obtain a new plasmon branch, , along the Brillouin Zone. In particular, we have found that it goes to
zero near {\bf Q}
Orbital ordering in charge transfer insulators
We discuss a new mechanism of orbital ordering, which in charge transfer
insulators is more important than the usual exchange interactions and which can
make the very type of the ground state of a charge transfer insulator, i.e. its
orbital and magnetic ordering, different from that of a Mott-Hubbard insulator.
This purely electronic mechanism allows us to explain why orbitals in
Jahn-Teller materials typically order at higher temperatures than spins, and to
understand the type of orbital ordering in a number of materials, e.g.
K_2CuF_4, without invoking the electron-lattice interaction.Comment: 4 pages, 2 figure
Relation between the one-particle spectral function and dynamic spin susceptibility in superconducting BiSrCaCuO
Angle resolved photoemission spectroscopy (ARPES) provides a detailed view of
the renormalized band structure and, consequently, is a key to the self-energy
and the single-particle Green's function. Here we summarize the ARPES data
accumulated over the whole Brillouin zone for the optimally doped
BiSrCaCuO into a parametric model of the Green's
function, which we use for calculating the itinerant component of the dynamic
spin susceptibility in absolute units with many-body effects taken into
account. By comparison with inelastic neutron scattering (INS) data we show
that the itinerant component of the spin response can account for the integral
intensity of the experimental INS spectrum. Taking into account the bi-layer
splitting, we explain the magnetic resonances in the acoustic (odd) and optic
(even) INS channels.Comment: Submitted to PR
Incommensurate magnetic fluctuations and Fermi surface topology in LiFeAs
Using the angle-resolved photoemission spectroscopy (ARPES) data accumulated
over the whole Brillouin zone (BZ) in LiFeAs we analyze the itinerant component
of the dynamic spin susceptibility in this system in the normal and
superconducting state. We identify the origin of the incommensurate magnetic
inelastic neutron scattering (INS) intensity as scattering between the electron
pockets, centered around the point of the BZ and the large
two-dimensional hole pocket, centered around the -point of the BZ. As
the magnitude of the superconducting gap within the large hole pocket is
relatively small and angle dependent, we interpret the INS data in the
superconducting state as a renormalization of the particle-hole continuum
rather than a true spin exciton. Our comparison indicates that the INS data can
be reasonably well described by both the sign changing symmetry of the
superconducting gap between electron and hole pockets as well as sign
preserving gap, depending on the assumptions made for the fermionic damping.Comment: 7 pages, 5 figure
Determination of the necessary degree of national programs standardization by network and business planning methods
The article considers the application of methods that make it possible to determine the need for deeper standardization of processes within the framework of the implementation of national programs, based on the influence of the degree of standardization on the time and resource intensity of the implementation of national programs. To determine the impact of the degree of standardization on the implementation time of national programs implementation, it is proposed to use network-planning methods, taking into account the influence of the time required for the development and implementation of additional standards on the implementation of the national program. The impact of standardization on the resource intensity indicators of the implementation of national programs is proposed to be taken into account through the analysis of the dynamics of the amount of finance required for the implementation of the program. For this purpose, it is proposed to use business planning methods, namely: calculation of the costs associated with the development and implementation of additional standards and calculation of the financial benefits from deepening standardization, based on the calculation of the amount of reduction in the cost of financial resources per unit of the result of the national program implementation
Magnetic susceptibility of YbRh2Si2 and YbIr2Si2 on the basis of a localized 4f electron approach
We consider the local properties of the Yb3+ ion in the crystal electric
field in the Kondo lattice compounds YbRh2Si2 and YbIr2Si2. On this basis we
have calculated the magnetic susceptibility taking into account the Kondo
interaction in the simplest molecular field approximation. The resulting
Curie-Weiss law and Van Vleck susceptibilities could be excellently fitted to
experimental results in a wide temperature interval where thermodynamic and
transport properties show non-Fermi-liquid behaviour for these materials.Comment: 12 pages, 4 figures, 4 table
Renormalization of the elementary excitations in hole- and electron-doped cuprates due to spin fluctuations
Extending our previous studies we present results for the doping-, momentum-,
frequency-, and temperature- dependence of the kink-like change of the
quasiparticle velocity resulting from the coupling to spin fluctuations. In the
nodal direction a kink is found in both the normal and superconducting state
while in the antinodal direction a kink occurs only below due to the
opening of the superconducting gap. A pronounced kink is obtained only for
hole-doped, but not for electron-doped cuprates and is characteristically
different from what is expected due to electron-phonon interaction. We further
demonstrate that the kink structure is intimately connected to the resonance
peak seen in inelastic neutron scattering. Our results suggest similar effects
in other unconventional superconductors like .Comment: revised version, 12 pages, 19 figures. accepted for publication in
PR
Polygonal Structures in the Gaseous Disk: Numerical Simulations
The results of numerical simulations of a gaseous disk in the potential of a
stellar spiral density wave are presented. The conditions under which
straightened spiral arm segments (rows) form in the gas component are studied.
These features of the spiral structure were identified in a series of works by
A.D. Chernin with coauthors. Gas-dynamic simulations have been performed for a
wide range of model parameters: the pitch angle of the spiral pattern, the
amplitude of the stellar spiral density wave, the disk rotation speed, and the
temperature of the gas component. The results of 2D- and 3D-disk simulations
are compared. The rows in the numerical simulations are shown to be an
essentially nonstationary phenomenon. A statistical analysis of the
distribution of geometric parameters for spiral patterns with rows in the
observed galaxies and the constructed hydrodynamic models shows good agreement.
In particular, the numerical simulations and observations of galaxies give
for the average angles between straight segments.Comment: 22 pages, 10 figure
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