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

By Matteo D'Astuto, Matteo Calandra, Stephanie Reich, Abhay Shukla, Michele Lazzeri, Francesco Mauri, Janusz Karpinski, N.D. Zhigadlo, Alexei Bossak and Michael Krisch

Abstract

International audienceWe 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

Topics: magnesium compounds, type II superconductors, anharmonic lattice modes, X-ray scattering, Raman spectra, ab initio calculations, phonon spectra, PACS: 74.70.Ad, 74.25.Kc, 63.20.Dj, 63.20.Kr
Publisher: American Physical Society
Year: 2007
DOI identifier: 10.1103/PhysRevB.75.174508
OAI identifier: oai:HAL:hal-00146638v1
Provided by: Hal-Diderot
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