Four-well tunneling states and elastic response of clathrates

I. Zerec; V. Keppens; M. A. McGuire; D. Mandrus; B. C. Sales; P. Thalmeier

doi:10.1103/PhysRevLett.92.185502

Four-well tunneling states and elastic response of clathrates

I. Zerec, V. Keppens, M. A. McGuire, D. Mandrus, B. C. Sales, P. Thalmeier

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Abstract

The resonant ultrasound elastic constant measurements of the Eu ₈Ga₁₆Ge₃₀ and Sr₈Ga ₁₆Ge₃₀ clathrates were investigated. Described by two nearly degenerate four level systems (FLS), the elastic response of the Eu clathrates provides clear evidence for the existence of a new type of four-well tunneling states. Realistic potential was used to to estimate the tunneling frequencies. The harmonic oscillator type specific heat is explained by the energy gap between the two FLS's. Further, the pronounced depression observed in elastic constant measurements is explained by the quadrupolar interaction of FLS's with elastic strain.

Original language	English
Article number	185502
Pages (from-to)	185502-1-185502-4
Journal	Physical Review Letters
Volume	92
Issue number	18
DOIs	https://doi.org/10.1103/PhysRevLett.92.185502
State	Published - May 7 2004
Externally published	Yes

Funding

V. K. acknowledges support from NSF Grant No. DMR0206625. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725.

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10.1103/PhysRevLett.92.185502

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abstract = "The resonant ultrasound elastic constant measurements of the Eu 8Ga16Ge30 and Sr8Ga 16Ge30 clathrates were investigated. Described by two nearly degenerate four level systems (FLS), the elastic response of the Eu clathrates provides clear evidence for the existence of a new type of four-well tunneling states. Realistic potential was used to to estimate the tunneling frequencies. The harmonic oscillator type specific heat is explained by the energy gap between the two FLS's. Further, the pronounced depression observed in elastic constant measurements is explained by the quadrupolar interaction of FLS's with elastic strain.",

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AU - Sales, B. C.

AU - Thalmeier, P.

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Four-well tunneling states and elastic response of clathrates

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