NMR relaxation and resistivity from rattling phonons in pyrochlore superconductors

TL;DR

This paper models how rattling phonons in pyrochlore superconductors influence NMR relaxation and resistivity, revealing unique temperature dependencies that align with experimental data.

Contribution

It introduces a theoretical framework for understanding the impact of anharmonic phonons on NMR and resistivity in pyrochlore superconductors, emphasizing the dominance of two-phonon Raman processes.

Findings

NMR relaxation rate peaks at low temperature and saturates at high temperature.

Electrical resistivity exhibits T^2 dependence at low T and sqrt(T) at high T.

Results qualitatively match recent experimental observations.

Abstract

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.