We calculate the temperature dependence of NMR relaxation rate and electrical resistivity for coupling to a local, strongly anharmonic phonon mode. We argue that the two-phonon Raman process is dominating NMR relaxation. Due to the strong anharmonicity of the phonon an unusual temperature dependence is found having a low temperature peak and becoming constant towards higher temperatures. The electrical resistivity is found to vary like T^2 at low temperatures and following a sqrt{T} behavior at high temperatures. Both results are in qualitative agreement with recent observations on beta-pyrochlore oxide superconductors.
@article{arxiv.0706.4345,
title = {NMR relaxation and resistivity from rattling phonons in pyrochlore superconductors},
author = {Thomas Dahm and Kazuo Ueda},
journal= {arXiv preprint arXiv:0706.4345},
year = {2007}
}
Comments: 4 pages, 4 figures; new version with some minor additional clarifications; accepted for publication in Phys. Rev. Lett