日時：２０１3年9月2日(月)　午前10：00～11：00
場所：物性研究所本館　６階　A615
講師 : Hannu Mutka 氏 (Institut Laue Langevin)

題目：Anharmonic phonon response of encaged atoms investigated with neutron scattering

要旨：

Einstein modes witnessed by bulk thermodynamic data have initiated extensive investigation of low-energy phonon response, so–called ‘rattling’ modes. This phenomenology has been recently observed in skutterudites, clathrates as well as in β -pyrochlore osmates. Inelastic neutron scattering on powder samples has been applied in the search for microscopic evidence

of the Einstein modes as well as their anharmonicity. I shall review the experimental analysis of low-energy vibrational modes associated with the alkali atoms in the β-pyrochlores [1-5] and M atoms in the MxV2Al20 compounds, ‘Einstein’ solids first reported some 40 years ago and re-examined again recently [6]. The aim is to connect quantitatively the signature of the flat bottom potential seen as the hardening of the characteristic energy scale of the ‘rattling’ mode with increasing temperature and the corresponding downward, concave curvature in the T-dependence of the atomic displacement parameter <u2(T)>.