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arXiv · 0705.2615

Effects of Rattling Phonons on the Quasiparticle Excitation and Dynamics in the Superconducting $β$-Pyrochlore KOs$_2$O$_6$

Y. Shimono·T. Shibauchi·Y. Kasahara·T. Kato·K. Hashimoto·Y. Matsuda·J. Yamaura·Y. Nagao·Z. Hiroi
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Abstract

Microwave penetration depth $λ$ and surface resistance at 27 GHz are measured in high quality crystals of KOs$_2$O$_6$. Firm evidence for fully-gapped superconductivity is provided from $λ(T)$. Below the second transition at $T_{\rm p}\sim 8$ K, the superfluid density shows a step-like change with a suppression of effective critical temperature $T_{\rm c}$. Concurrently, the extracted quasiparticle scattering time shows a steep enhancement, indicating a strong coupling between the anomalous rattling motion of K ions and quasiparticles. The results imply that the rattling phonons help to enhance superconductivity, and that K sites freeze to an ordered state with long quasiparticle mean free path below $T_{\rm p}$.

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Y. Shimono, T. Shibauchi, Y. Kasahara, T. Kato, K. Hashimoto, Y. Matsuda, J. Yamaura, Y. Nagao, Z. Hiroi. 2007-05-17. Effects of Rattling Phonons on the Quasiparticle Excitation and Dynamics in the Superconducting $β$-Pyrochlore KOs$_2$O$_6$. https://doi.org/10.1103/physrevlett.98.257004

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