M. d'Astuto

Phonon dispersion and lifetimes in MgB2

We measure phonon dispersion and linewidth in a single crystal of MgB2 along the Gamma-A, Gamma-M, and A-L directions using inelastic x-ray scattering. We use density functional theory to compute the effect of both electron-phonon coupling and anharmonicity on the linewidth, obtaining excellent agreement with experiment. Anomalous broadening of the E(2g) phonon mode is found all along Gamma-A. The dominant contribution to the linewidth is always the electron-phonon coupling.

Bond stretching phonon softening and kinks in the angle-resolved photoemission spectra of optimally doped Bi2Sr1.6La0.4Cu2O6+delta superconductors.

We report the first measurement of the Cu-O bond stretching phonon dispersion in optimally doped Bi2Sr1.6La0.4Cu2O6+delta using inelastic x-ray scattering. We found a softening of this phonon at q=( approximately 0.25,0,0) from 76 to 60 meV, similar to the one reported in other cuprates. A comparison with angle-resolved photoemission data on the same sample revealed an excellent agreement in terms of energy and momentum between the angle-resolved photoemission nodal kink and the soft part of the bond stretching phonon. Indeed, we find that the momentum space where a 63+/-5 meV kink is observed can be connected with a vector q=(xi,0,0) with xi > or =0.22, corresponding exactly to the soft part of the bond stretching phonon.

Anomalous dispersion of longitudinal optical phonons in Nd(1.86)Ce(0.14)CuO(4+delta) determined by inelastic x-ray scattering.

The phonon dispersions of Nd(1.86)Ce(0.14)CuO(4+delta) along the [xi,0,0] direction have been determined by inelastic x-ray scattering. Compared to the undoped parent compound, the two highest longitudinal phonon branches, associated with the Cu-O bond stretching and out-of-plane oxygen vibration, are shifted to lower energies. Moreover, an anomalous softening of the bond-stretching band is observed at about q = (0.2,0,0). These signatures provide evidence for strong electron-phonon coupling in this electron-doped high-temperature superconductor.

Weak anharmonic effects in MgB2: A comparative inelastic x-ray scattering and Raman study

We study anharmonic effects in MgB2 by comparing inelastic x-ray and Raman scattering together with ab initio calculations. Using high-statistics and high-q-resolution measurements we show that the E2g-mode linewidth is independent of temperature along Gamma-A. We show, contrary to previous claims, that the Raman-peak energy decreases as a function of increasing temperature, a behavior inconsistent with all the anharmonic ab initio calculations of the E2g mode at Gamma available in the literature. These findings and the excellent agreement between the x-ray-measured and ab initio—calculated phonon spectra suggest that anharmonicity is not the main mechanism determining the temperature behavior of the Raman-peak energy. The Raman-E2g-peak position and linewidth can be explained by large dynamical effects in the phonon self-energy. In light of the present findings, the commonly accepted explanation of the reduced isotope effect in terms of anharmonic effects needs to be reconsidered.

Sharp optical-phonon softening near optimal doping in La2-xBaxCUO4+δ observed via inelastic x-ray scattering

Matteo d’Astuto, ∗ Guy Dhalenne, Jeff Graf, Moritz Hoesch, Paola Giura, Michael Krisch, Patrick Berthet, Alessandra Lanzara, 5 and Abhay Shukla Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), Université Pierre et Marie Curie Paris 6, case 115, 4, place Jussieu, 75252 Paris cedex 05, France Laboratoire de Physico-Chimie de l’Etat Solide (ICMMO), CNRS UMR8182, Université Paris-Sud 11, Bâtiment 410, 91405 Orsay, France Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France Department of Physics, University of California Berkeley, CA 94720, USA (Dated: October 1, 2008)

Energy calibration of a high-resolution inelastic x-ray scattering spectrometer

The energy scale of a triple-axis x-ray spectrometer with meV energy resolution based on perfect silicon crystal optics is calibrated, utilizing the most recent determination of the silicon lattice parameter and its thermal expansion coefficient and recording the dispersion of longitudinal acoustic and optical phonons in a diamond single crystal and the molecular vibration mode in liquid nitrogen. Comparison of the x-ray results with previous inelastic neutron and Raman scattering results as well as with ab initio phonon dispersion calculations yields an overall agreement better than 2%.

Phonon dispersion and low-energy anomaly in CaC6 from inelastic neutron and x-ray scattering experiments

We report measurements of phonon dispersion in CaC

Phonon anomalies and lattice dynamics in superconducting oxychlorides Ca

_6

_{2-x}

using inelastic X-ray and neutron scattering. We find good overall agreement, particularly in the 50 meV energy region, between experimental data and first-principles density-functional-theory calculations. However, on the longitudinal dispersion along the

CuO

(1 1 1)