Optical conductivity of rattling phonons in type-I clathrate Ba8 Ga16 Ge30

T. Mori, S. Goshima, K. Iwamoto, S. Kushibiki, H. Matsumoto, N. Toyota, K. Suekuni, M. A. Avila, T. Takabatake, T. Hasegawa, N. Ogita, M. Udagawa

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Abstract

A series of infrared-active optical phonons have been detected in type-I clathrate Ba8 Ga16 Ge30 by terahertz time-domain spectroscopy. The conductivity spectra with the lowest-lying peaks at 1.15 and 1.80 THz are identified with the so-called rattling phonons, i.e., optical modes of the guest ion Ba2+ (2) with T1u symmetry in the oversized tetrakaidecahedral cage. The temperature dependence of the spectra from these modes are totally consistent with calculations based on a one-dimensional anharmonic potential model that, with decreasing temperature, the shape becomes asymmetrically sharp associated with a softening for the weight to shift to lower frequency. These temperature dependences are determined, without any interaction effects, by the Bose factor for optical excitations of anharmonic phonons with the nonequally spaced energy levels.

Original languageEnglish
Article number212301
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume79
Issue number21
DOIs
Publication statusPublished - Jun 12 2009
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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    Mori, T., Goshima, S., Iwamoto, K., Kushibiki, S., Matsumoto, H., Toyota, N., Suekuni, K., Avila, M. A., Takabatake, T., Hasegawa, T., Ogita, N., & Udagawa, M. (2009). Optical conductivity of rattling phonons in type-I clathrate Ba8 Ga16 Ge30. Physical Review B - Condensed Matter and Materials Physics, 79(21), [212301]. https://doi.org/10.1103/PhysRevB.79.212301