R. Monnier - Academia.edu (original) (raw)

Papers by R. Monnier

Philosophical Magazine Part B, 1997

Abstract The progress in the first-principles determination of the thermal equilibrium concentrat... more Abstract The progress in the first-principles determination of the thermal equilibrium concentration profile at the surface of a random binary alloy is reviewed. After a brief introduction to the (single-site) coherent-potential approximation used to model concentrated alloys, and to the elements of density functional theory necessary for the ab initio treatment of such systems, three self-consistent Green function techniques for calculating ground-state properties of random alloy surfaces, namely the layer Korringa-Kohn-Rostoker (KKR), the screened KKR and the tight-binding linear muffin-tin orbital (LMTO) method are presented, with particular emphasis on the relationship between the latter two approaches. Although each of these methods is capable of yielding the internal energy of the system for any given profile, a ‘brute force’ search for the optimum configuration is unrealistic, in view of the large number of possibilities available. Instead, one uses the results of the above self-consistent calculat...

Physical Review B, 1978

By analogy with the change-in-self-consistent-field (hSCF) method of atomic physics, the work fun... more By analogy with the change-in-self-consistent-field (hSCF) method of atomic physics, the work function of a metal surface is computed as the difference between the total energy of the system in its final state, where one electron is missing from the metal and removed to a large distance from the surface, and its initial state, where the metal is charge neutral. Our hSCF expression is a generalization of one given by Lang and Kohn, who assumed the electron density profile to be that of a jellium surface. The ASCF expression also reduces in the appropriate limit to an expression derived by Mahan and Schaich. We show that the bSCF expression is much less profile-sensitive than other exact expressions for the work function and is therefore well suited for use with approximate profiles. We apply our "variational self-consistent" profiles (more realistic than jellium profiles) to evaluate the hSCF work function for a few selected surfaces of simple metals, among them the three low-index faces of Al, for which agreement with experiment is found to be good.

Philosophical Magazine A, 1993

Abstract Stacking fault energies in dilute Cu(Al) alloys and across the composition range of PdAg... more Abstract Stacking fault energies in dilute Cu(Al) alloys and across the composition range of PdAg alloys are calculated from first principles using the layer Korringa-Kohn-Rostoker method and treating the compositional disorder within the coherent potential approximation. In Cu(Al), rigid-band behaviour results in a sharp reduction in the fault energy with Al concentration. The non-uniform variation of the fault energy in PdAg is understood in terms of the relative band-widths and d-resonance energies of Pd and Ag.

The surface electronic structure of UHV-cleaved divalent hexaboride EuB6 is investigated using an... more The surface electronic structure of UHV-cleaved divalent hexaboride EuB6 is investigated using angle-resolved photoemission and the time-dependence of the Eu 4d-character X-point electron pocket, B-p band structure and Eu 4f states are characterized. Surface-slab LDA calculations allow identification in the data of a distinct surface-related band residing in the bulk-projected band gap along X-M and energy-shifted surface-atom Eu 4f states

Le Journal de Physique Colloques, 1987

Physical Review Letters, 1986

A method is presented for computing the mixing parameters in the Anderson model for heavy-rare-ea... more A method is presented for computing the mixing parameters in the Anderson model for heavy-rare-earth compounds, based on a linear combination of atomic orbitals fit to a self-consistent band-structure calculation. An appropriate average of these parameters is used in a many-body calculation of the valence-band-x-ray-photoemission and inverse-photoemission spectra of YbP, with the Coulomb integral U as the only adjustable quantity. The calculated inverse-photoemission spectrum agrees qualitatively with room-temperature low-resolution data by Baer et al.

Applied Physics Letters, 1983

ABSTRACT

Physical Review Letters, 2001

The formation energy and local magnetic moment of a series of point defects in CaB 6 are computed... more The formation energy and local magnetic moment of a series of point defects in CaB 6 are computed using a supercell approach within the generalized gradient approximation to density functional theory. Based on these results, speculations are made as to the influence of these defects on electrical transport. It is found that the substitution of Ca by La does not lead to the formation of a local moment, while a neutral B 6 vacancy carries a moment of 2.4 Bohr magnetons, mostly distributed over the six nearest-neighbour B atoms. A plausible mechanism for the ferromagnetic ordering of these moments is suggested. Since the same broken B-B bonds appear on the preferred (100) cleavage planes of the CaB 6 structure, it is argued that internal surfaces in polycrystals as well as external surfaces in general will make a large contribution to the observed magnetization.

La variation de la vitesse de diffusion des electrons de conduction sur la couche electronique de... more La variation de la vitesse de diffusion des electrons de conduction sur la couche electronique de la troisieme bande de la surface de Fermi de l'aluminium due a de faibles concentrations en impuretes lithium a ete determinee a partir d'etudes d'effet de Haas van Alphen

Presentation de resultats pour la resistivite longitudinale et transversale de fils supraconducte... more Presentation de resultats pour la resistivite longitudinale et transversale de fils supraconducteurs multifilamentaires a l'etat normal en fonction du libre parcours moyen en volume dans le materiau de la matrice, du rayon des filaments et de la distance entre eux. Les effets dimensionnels semblent jouer un role important dans les parametres caracteristiques des supraconducteurs techniques

Physical Review B

A number of recent experiments report the low-temperature thermopower α and specific heat coeffic... more A number of recent experiments report the low-temperature thermopower α and specific heat coefficients γ = CV /T of strongly correlated electron systems. Describing the charge and heat transport in a thermoelectric by transport equations, and assuming that the charge current and the heat current densities are proportional to the number density of the charge carriers, we obtain a simple mean-field relationship between α and the entropy density S of the charge carriers. We discuss corrections to this mean-field formula and use results obtained for the periodic Anderson and the Falicov-Kimball models to explain the concentration (chemical pressure) and temperature dependence of α/γT in EuCu2(Ge1−xSix)2, CePt1−xNix, and YbIn1−xAgxCu4 intermetallic compounds. We also show, using the 'poor man's mapping' which approximates the periodic Anderson lattice by the single impurity Anderson model, that the seemingly complicated behavior of α(T) can be explained in simple terms and that the temperature dependence of α(T) at each doping level is consistent with the magnetic character of 4f ions.

Anisotropic impurity-induced scattering rates and their orbital averages (Dingle temperatures) ar... more Anisotropic impurity-induced scattering rates and their orbital averages (Dingle temperatures) are expressed in terms of a set of coefficients determined by the band structure of the pure host, and phase shift parameters describing the scattering from a specific impurity. We have evaluated the former set of coefficients in a previous multiple-plane-wave based calculation for dilute Al-Li. The calculation of Li-induced phase shifts was a self-consistent one based on the density functional formalism, but neglected lattice backscattering effects. In order to include the latter we use the so-called Friedel phase shifts obtained from a KKR Green's function calculation, together with the previously calculated host band structure coefficients in a mixed ab-initio calculation of the Dingle temperatures. The agreement with experiment is improved considerably. The effects of alternative refinements to our previous calculation (e.g. the inclusion of nonlocal exchange and correlation) are d...

Journal of Physics: Condensed Matter, 2005

The pressure-induced changes in the temperature-dependent thermopower S(T) and electrical resisti... more The pressure-induced changes in the temperature-dependent thermopower S(T) and electrical resistivity ρ(T) of CeRu2Ge2 are described within the single-site Anderson model. The Ce-ions are treated as impurities and the coherent scattering on different Ce-sites is neglected. Changing the hybridisation Γ between the 4f-states and the conduction band accounts for the pressure effect. The transport coefficients are calculated in the non-crossing approximation above the phase boundary line. The theoretical S(T) and ρ(T) curves show many features of the experimental data. The seemingly complicated temperature dependence of S(T) and ρ(T), and their evolution as a function of pressure, is related to the crossovers between various fixed points of the model.

Journal of Physics C: Solid State Physics

The equilibrium lattice configuration, electronic excitation energies and activation energies for... more The equilibrium lattice configuration, electronic excitation energies and activation energies for hopping motion are calculated for a self-trapped hole in simple cubic CsC1, CsBr and CsI. The defect is regarded as a X; molecular ion (X = Cl. Br. I) whose bond-length has been modified by the crystalline environment. Agreement with the experimental ultraviolet transition energies is good. Excitation energies deduced from measurement of g shifts in CsBr and CsI are too low, a feature common to all alkali bromides and iodides, and attributed to the approximations involved in their derivation. The initial calculations predict lower activation energies for 90" jumps than for 180"jumps, in contrast with what is observed in CsI. An alternative model is presented, which reproduces the correct trend. Comparison of the actual numbers with experiment is hampered by the fact that the latter are done at low temperature (60-90K), the calculations being done in the high-temperature limit.

We report on a Raman scattering investigation of the charge-density-wave (CDW), quasi two-dimensi... more We report on a Raman scattering investigation of the charge-density-wave (CDW), quasi two-dimensional rare-earth tri-tellurides RTe3 (R= La, Ce, Pr, Nd, Sm, Gd and Dy) at ambient pressure, and of LaTe3 and CeTe3 under externally applied pressure. The observed phonon peaks can be ascribed to the Raman active modes for both the undistorted as well as the distorted lattice in

Physical Review B, 2001

We report on measurements of the specific heat of the recently discovered superconductor MgB2 in ... more We report on measurements of the specific heat of the recently discovered superconductor MgB2 in the temperature range between 3 and 220 K. Based on a modified Debye-Einstein model, we have achieved a rather accurate account of the lattice contribution to the specific heat, which allows us to separate the electronic contribution from the total measured specific heat. From our result for the electronic specific heat, we estimate the electron-phonon coupling constant λ to be of the order of 2, significantly enhanced compared to common weak-coupling values ≤ 0.4. Our data also indicate that the electronic specific heat in the superconducting state of MgB2 can be accounted for by a conventional, s-wave type BCS-model.