Phonon widths versus pressure

Abstract

In the course of a few years before his untimely death, Jean Michel Besson and his group performed the most comprehensive and detailed studies of the phonon dispersion relations of semiconductors on pressure using inelastic neutron scattering (INS). Because of the intrinsically poor resolution of this technique, parallel studies of phonon line widths are well-nigh impossible. Such studies would be of considerable interest for revealing ubiquitous anomalies in the phonon self-energies, but so far they have been confined to k -points near the center of the Brillouin zone, as required by laser Raman spectroscopy. Some interesting results obtained in this manner are presented. The possibility of simulating the effects of high pressure by changing the isotopic composition of the material will also be touched upon. It is hoped that recent developments and activity concerning the technique of Neutron Spin Echo spectroscopy will open new possibilities for using Besson's cells for the determination of the pressure dependence of phonon line widths.

Keywords:

• Phonon widths
• Pressure dependence
• Stable isotopes
• Anharmonicity
• Tetrahedral semiconductors

Acknowledgements

I would like to acknowledge the continued collaboration of K. Syassen and B. A. Weinstein in performing pressure measurements and interpreting the line width data. Thanks are also due to A. Debernardi for the ab initio line width calculations and to many other collaborators whose number is too large to mention them explicitly. Their names can be found in the references.