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NMR Observation of Rattling Phonons in the Pyrochlore Superconductor KOs2O6

M. Yoshida·K. Arai·R. Kaido·M. Takigawa·S. Yonezawa·Y. Muraoka·Z. Hiroi
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Abstract

We report nuclear magnetic resonance studies on the beta-pyrochlore oxide superconductor KOs2O6. The nuclear relaxation at the K sites is entirely caused by fluctuations of electric field gradient, which we ascribe to highly anharmonic low frequency oscillation (rattling) of K ions. A phenomenological analysis shows a crossover from overdamped to underdamped behavior of the rattling phonons with decreasing temperature and its sudden sharpening below the superconducting transition temperature Tc. Absence of the Hebel-Slichter peak in the relaxation rate at the O sites below Tc also indicates strong electron-phonon coupling.

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M. Yoshida, K. Arai, R. Kaido, M. Takigawa, S. Yonezawa, Y. Muraoka, Z. Hiroi. 2007-05-09. NMR Observation of Rattling Phonons in the Pyrochlore Superconductor KOs2O6. https://doi.org/10.1103/physrevlett.98.197002

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