Optical conductivity spectral anomalies in the off-center rattling system β-Ba8Ga16Sn30

T. Mori, K. Iwamoto, S. Kushibiki, H. Honda, H. Matsumoto, N. Toyota, M. A. Avila, K. Suekuni, T. Takabatake

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Abstract

We present optical conductivity studies of the type-I clathrate Ba 8Ga16Sn30, using a terahertz time-domain spectrometer (0.3-3.0 THz). The lowest-lying spectral peak at 0.72 THz due to the Ba(2) ion's off-center vibration in the oversized cage shows a drastic and anomalous temperature dependence. Below about 100 K, the single broad peak splits into two subpeaks, and with further lowering of the temperature, the spectral shape of this so-called rattling phonon shows non-Boltzmann broadening to the point that the linewidth becomes comparable to the peak frequency. Whereas the initial splitting can be understood by assuming a multiwell anharmonic potential, the strong linewidth broadening toward low temperature cannot, since the Boltzmann factor generally sharpens the low-temperature spectra. The observed behavior suggests strong interaction between the local anharmonic phonons and other excitations.

Original languageEnglish
Article number015501
JournalPhysical review letters
Volume106
Issue number1
DOIs
Publication statusPublished - 2011

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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    Mori, T., Iwamoto, K., Kushibiki, S., Honda, H., Matsumoto, H., Toyota, N., Avila, M. A., Suekuni, K., & Takabatake, T. (2011). Optical conductivity spectral anomalies in the off-center rattling system β-Ba8Ga16Sn30. Physical review letters, 106(1), [015501]. https://doi.org/10.1103/PhysRevLett.106.015501