F. Vernay

Evidence for weak electronic correlations in iron pnictides

Using x-ray absorption and resonant inelastic x-ray scattering, charge dynamics at and near the Fe L edges is investigated in Fe pnictide materials, and contrasted to that measured in other Fe compounds. It is shown that the XAS and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar to Fe metal. Cluster diagonalization, multiplet, and density-functional calculations show that Coulomb correlations are much smaller than in the cuprates, highlighting the role of Fe metallicity and strong covalency in these materials. Best agreement with experiment is obtained using Hubbard parameters U <~;; 2eV and J ~;; 0.8eV.

Systematic study of electron-phonon coupling to oxygen modes across the cuprates

The large variations of T

Systematic computation of crystal-field multiplets for x-ray core spectroscopies

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Orbital degeneracy as a source of frustration in LiNiO2

across the cuprate families is one of the major unsolved puzzles in condensed matter physics, and is poorly understood. Although there appears to be a great deal of universality in the cuprates, several orders of magnitude changes in T

Interplay between surface anisotropy and dipolar interactions in an assembly of nanomagnets

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Spin configurations in hard/soft coupled bilayer systems: Transitions from rigid magnet to exchange-spring

can be achieved through changes in the chemical composition and structure of the unit cell. In this paper we formulate a systematic examination of the variations in electron-phonon coupling to oxygen phonons in the cuprates, incorporating a number of effects arising from several aspects of chemical composition and doping across cuprate families. It is argued that the electron-phonon coupling is a very sensitive probe of the material-dependent variations of chemical structure, affecting the orbital character of the band crossing the Fermi level, the strength of local electric fields arising from structural-induced symmetry breaking, doping dependent changes in the underlying band structure, and ionicity of the crystal governing the ability of the material to screen

Unraveling the nature of charge excitations in La2CuO4 with momentum-resolved Cu K-edge resonant inelastic X-ray scattering

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Antiferromagnetic Spin-S Chains with Exactly Dimerized Ground States

-axis perturbations. Using electrostatic Ewald calculations and known experimental structural data, we establish a connection between the materials maximal T

AC susceptibility of an assembly of nanomagnets: combined effects of surface anisotropy and dipolar interactions

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Cu

at optimal doping and the strength of coupling to