Anomalous infrared spectra of hybridized phonons in type-I clathrate Ba${}_8$Ga${}_{16}$Ge${}_{30}$

Abstract

The optical conductivity spectra of the rattling phonons in the clathrate Ba${}_8$Ga${}_{16}$Ge${}_{30}$ are investigated in detail by use of the terahertz time-domain spectroscopy. The experiment has revealed that the lowest-lying vibrational mode of a Ba(2)${}^{2+}$ ion consists of a sharp Lorentzian peak at 1.2 THz superimposed on a broad tail weighted in the lower frequency regime around 1.0 THz. With decreasing temperature, an unexpected linewidth broadening of the phonon peak is observed, together with monotonic softening of the phonon peak and the enhancement of the tail structure. These observed anomalies are discussed in terms of impurity scattering effects on the hybridized phonon system of rattling and acoustic phonons.

Submitted to JPSJ

References in corpus (4)

• Glasslike vs. crystalline thermal conductivity in carrier-tuned Ba8Ga16X30 clathrates (X = Ge, Sn)
• NMR relaxation and resistivity from rattling phonons in pyrochlore superconductors
• Optical self-energy of superconducting Pb in the THz region
• Significance of Off-Center Rattling for Emerging Low-lying THz Modes in type-I Clathrates

Cited by in corpus (2)

• Phonon-glass electron-crystal thermoelectric clathrates: Experiments and theory
• Thermal conductivity in intermetallic clathrates: A first principles perspective