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Anharmonic effects in MgB2? A comparative inelastic X-ray scattering and Raman study

Matteo d'Astuto·Matteo Calandra·Stephanie Reich·Abhay Shukla·Michele Lazzeri·Francesco Mauri·Janusz Karpinski·N. D. Zhigadlo·Alexei Bossak·Michael Krisch
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Abstract

We study anharmonic effects in MgB2 by comparing Inelastic X-ray and Ramanscattering 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 behaviour inconsistent with all the anharmonic ab-initio calculations of the E2g mode at Gamma available in 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 behaviour 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.

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Matteo d'Astuto, Matteo Calandra, Stephanie Reich, Abhay Shukla, Michele Lazzeri, Francesco Mauri, Janusz Karpinski, N. D. Zhigadlo, Alexei Bossak, Michael Krisch. 2007-03-05. Anharmonic effects in MgB2? A comparative inelastic X-ray scattering and Raman study. https://doi.org/10.1103/physrevb.75.174508

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