1,721,190 research outputs found
Jahn-Teller and Coulomb correlations in fullerene ions and compounds : from isolated ions to metal, insulator, and superconductor phases of alkali fulleride solids
No full textWe offer a partial review of some theoretical aspects of the interplay among
strong electron-electron Coulomb plus exchange correlations and Jahn-Teller
vibronic phenomena in fullerene ions and in solid conductors, superconductors, insulators. The first half of this work covers molecular fullerene ions, their intra-molecular Jahn-Teller effect, Coulomb exchange (Hund's rule) interactions, and
molecular vibronic spectroscopies. Several aspects, calculations, and phenomena are discussed also in connection with spectroscopic data. The second part addresses intermolecular electron motion in
molecular solid fullerides, with special emphasis given to trivalent cases such as
K3C60 and NH3 K3C60, where metallic, superconducting and Mott insulating phases are at play. Dynamical mean field theory
approaches to simplified Hamiltonians for this system are discussed in the light of some of the observed phenomenology. In particular NH3 K3C60 and the more recently studied cubic Cs3C60 compounds are discussed as realizations of Mott-Jahn-Teller insulators, which, under pressure, turn into strongly correlated superconductors, sharing several important elements with the cuprate superconductors
Exact zero-point energy shift in the e circle times(nE), t circle times(nH) many-modes dynamic Jahn-Teller systems at strong coupling
No full textWe find the exact semiclassical (strong coupling) zero-point energy shifts applicable to the e x (nE) and t x (nH) dynamic Jahn-Teller problems, for an arbitrary number n of discrete vibrational modes simultaneously coupled to one single electronic level. We also obtain an analytical formula for the frequency of the resulting normal modes, which has an attractive and apparently general Slater-Koster form. The Limits of validity of this approach are assessed by comparison with O'Brien's previous effective-mode approach, and with accurate numerical diagonalizations. Numerical values obtained for t x (nH) with n = 8 and coupling constants appropriate to C-60(-) are used for this purpose, and are discussed in the context of fullerene
Lifetime for resonant tunneling in a transverse magnetic field
No full textWe present a numerical study of the time-dependent resonant tunneling of a Gaussian wave packet through a double-barrier structure in a transverse magnetic field. From the decay rate of the charge trapped in the quantum well, we obtain the field dependence of the lifetime τ0 of the resonant level. τ0 is found to exhibit an oscillatory behavior with increasing magnetic field. This effect is explained as due to the field-induced hybridization of the resonant level with the interfacial Landau states corresponding to the semiclassical skipping orbits at the barrier interfaces. An experiment which should allow the observation of such effects in real heterostructures is suggested
f-f excitations by resonant electron-exchange collisions in rare-earth metals
No full textThe spin-forbidden f-f multiplet excitations are observed for the first time as the strongest features in the electron-energy-loss spectra of Gd, Dy, and Sm metals at low primary-electron energies. The exchange nature of the excitation process is argued, in analogy with that of spin-flip Stoner excitations in d-band ferromagnets. A resonance enhancement observed for primary-electron energies near the 4d-4f core threshold is found to be consistent with the proposed mechanism
Surface Lattice-Dynamical Approach to the Reconstruction of W(100)
No full textWe review the surface reconstruction of the bcc (100) transition metal surface, particularly W(100) and some of the results obtained, with the method of the effective surface lattice dynamics
Kink plateau dynamics in finite-size lubricant chains
No full textWe extend the study of velocity quantization phenomena recently found in the classical motion of an idealized ID model solid lubricant -
consisting of a harmonic chain interposed between two periodic sliding potentials [A. Vanossi, M. Manini, G. Divitini, G.E. Santoro, E.
Tosatti, Phys. Rev. Lett. 97 (2006) 056101]. This quantization is due to
one slider rigidly dragging the commensurate lattice of kinks that the
chain forms with the other slider. In this follow-up work we consider
finite-size chains rather than infinite chains. The finite-size (i) permits the development of robust velocity plateaus as a function of the
lubricant stiffness, and (ii) allows an overall chain length re-adjustment which spontaneously promotes single-particle periodic oscillations. These periodic oscillations replace the quasiperiodic motion produced by general incommensurate periods of the sliders and the lubricant in the infinite-size model. Possible consequences of these results for some real systems are discussed
Reconstruction and Dynamics of the W(100), Mo(100) and Cr(100) Surfaces
No full textA model has been developed that is capable of describing the structural and lattice dynamical properties of the reconstructed W(100), and the closely related Mo(100) and Cr(100), surfaces. In particular the different reconstructions (both commensurate and incommensurate) that are seen on the clean neutral surface, on a high-field FIM tip and on H-covered surfaces, are found to belong to the same T equals O surface ′′phase diagram′′
Les greffes veineuses en microchirurgie reconstructrici pour le traitement des lynphoedemes
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