ELECTRON-PHONON INTERACTION IN SEMICONDUCTORS WITH UNSTABLE VALENCE

1993 ◽  
Vol 07 (01n03) ◽  
pp. 193-196 ◽  
Author(s):  
K. A. KIKOIN ◽  
A. S. MISHCHENKO
Keyword(s):  
Mixed Valence ◽  
Microscopic Theory ◽  
Electronic Excitations ◽  
Valence Fluctuations ◽  
Electron Phonon Interaction ◽  
Local Character ◽  
Phonon Spectra ◽  
Longitudinal Phonon ◽  
Scattering Spectra ◽  
Non Local

A microscopic theory for the interaction of lattice vibrations with electronic excitations specific to the intermediate valence semiconductors is proposed. The essentially non-local character of the valence shell excitations leads to the additional dispersion of the electron-phonon matrix elements, which give dramatic contribution to the form of longitudinal phonon branches anomalies. This description enlightens both the mechanism of phonon softening in perfect and imperfect lattices, appearance of extra modes in neutron scattering spectra and the nature of valence fluctuations in RE semiconductors. The phonon spectra of integer valence (EuS, SmS(B)) and mixed valence (Sm(Y)S, SmS(G), TmSe, SmB6) semiconductors are calculated within this unified approach.

Peculiarities of the Electron-Phonon Interaction in Graphite Containing Metallic Intercalated Layers

2010 ◽  
Vol 297-301 ◽  
pp. 75-81 ◽  
Author(s):  
Alexander Feher ◽  
S.B. Feodosyev ◽  
I.A. Gospodarev ◽  
V.I. Grishaev ◽  
K.V. Kravchenko ◽  
...  
Keyword(s):  
Jacobi Matrix ◽  
Local Density ◽  
Dynamic Properties ◽  
Electronic States ◽  
Bcs Theory ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Density Of Electronic States ◽  
Eliashberg Equation ◽  
Phonon Spectra

The calculation of the local density of electronic states of graphene with vacancies, using the method of Jacobi matrix, was performed. It was shown that for atoms in the sublattice with a vacancy the local density of electronic states conserves the Dirac singularity, similarly as in an ideal graphene. A quasi-Dirac singularity was observed also in the phonon spectra of graphite for the atom displacements in the direction perpendicular to layers. Changes of phonon spectra of graphite intercalated with various metals were analyzed. On the basis of our results and using the BCS theory and Eliashberg equation we proposed what dynamic properties an intercalated graphite system should show to obtain an increased Tc.

scholarly journals Turbulence through the Spyglass of Bilocal Kinetics

Entropy ◽  
2018 ◽  
Vol 20 (7) ◽  
pp. 539 ◽  
Author(s):  
Gregor Chliamovitch ◽  
Yann Thorimbert
Keyword(s):  
Turbulent Flows ◽  
Kinetic Scheme ◽  
Navier Stokes ◽  
Pressure Tensor ◽  
Kinetic Description ◽  
Balance Equations ◽  
Coupling Term ◽  
Navier Stokes Equation ◽  
Local Character ◽  
Non Local

In two recent papers we introduced a generalization of Boltzmann’s assumption of molecular chaos based on a criterion of maximum entropy, which allowed setting up a bilocal version of Boltzmann’s kinetic equation. The present paper aims to investigate how the essentially non-local character of turbulent flows can be addressed through this bilocal kinetic description, instead of the more standard approach through the local Euler/Navier–Stokes equation. Balance equations appropriate to this kinetic scheme are derived and closed so as to provide bilocal hydrodynamical equations at the non-viscous order. These equations essentially consist of two copies of the usual local equations, but coupled through a bilocal pressure tensor. Interestingly, our formalism automatically produces a closed transport equation for this coupling term.

scholarly journals Multiscalar moral economy

Focaal ◽  
2020 ◽  
pp. 1-14
Author(s):  
Tijo Salverda
Keyword(s):  
Moral Economy ◽  
Land Grabbing ◽  
Rural Residents ◽  
Local Character ◽  
Economic Exchanges ◽  
Local Actors ◽  
Non Local ◽  
Heuristic Device ◽  
Moral Economic

This article addresses the relevance of the moral economy concept in light of unequal socioeconomic relations between a European agribusiness and rural residents in Zambia. It argues that the moral economy concept offers a helpful heuristic device for analyzing how relationships are constituted, negotiated, and contested among interdependent actors with “opposing” socioeconomic interests. To explain the dynamics of their relationships, however, the moral economy concept has to extend beyond its usual, spatially restricted (i.e., local) focus. Instead, “external,” distant, non-local actors, such as foreign critics concerned about “land grabbing,” also influence the local character of moral-economic exchanges between the agribusiness and rural residents. Hence, the article proposes a multiscalar perspective to account for the influence of a wider array of actors.

scholarly journals Avoided valence transition in a plutonium superconductor

2015 ◽  
Vol 112 (11) ◽  
pp. 3285-3289 ◽  
Author(s):  
B. J. Ramshaw ◽  
Arkady Shekhter ◽  
Ross D. McDonald ◽  
Jon B. Betts ◽  
J. N. Mitchell ◽  
...  
Keyword(s):  
Heavy Fermion ◽  
Cuprate Superconductors ◽  
Critical Role ◽  
Mixed Valence ◽  
Magnetic Fluctuations ◽  
Elastic Symmetry ◽  
Valence Transition ◽  
Valence Fluctuations ◽  
Wide Range ◽  
Valence Electrons

The d and f electrons in correlated metals are often neither fully localized around their host nuclei nor fully itinerant. This localized/itinerant duality underlies the correlated electronic states of the high-Tc cuprate superconductors and the heavy-fermion intermetallics and is nowhere more apparent than in the 5f valence electrons of plutonium. Here, we report the full set of symmetry-resolved elastic moduli of PuCoGa5—the highest Tc superconductor of the heavy fermions (Tc = 18.5 K)—and find that the bulk modulus softens anomalously over a wide range in temperature above Tc. The elastic symmetry channel in which this softening occurs is characteristic of a valence instability—therefore, we identify the elastic softening with fluctuations of the plutonium 5f mixed-valence state. These valence fluctuations disappear when the superconducting gap opens at Tc, suggesting that electrons near the Fermi surface play an essential role in the mixed-valence physics of this system and that PuCoGa5 avoids a valence transition by entering the superconducting state. The lack of magnetism in PuCoGa5 has made it difficult to reconcile with most other heavy-fermion superconductors, where superconductivity is generally believed to be mediated by magnetic fluctuations. Our observations suggest that valence fluctuations play a critical role in the unusually high Tc of PuCoGa5.

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