Why is sound absorption by tunneling defects the same in all glasses? · revision history

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Title
Why is sound absorption by tunneling defects the same in all glasses?
Plain
In every glass tested, sound waves lose nearly the same small fraction of their energy per cycle at low temperature, within a factor of about twenty. The standard tunneling model fits this but gives no reason why the number should be universal.
Precise · changed · core
Revision 1: Below $\sim 1\,\mathrm{K}$ amorphous solids show specific heat $C \sim T$, thermal conductivity $\kappa \sim T^{2}$ and an internal-friction plateau $Q^{-1} = (\pi/2) C_{\mathrm{tun}}$, with tunneling strength $C_{\mathrm{tun}} = P \gamma^{2}/(\rho v^{2})$ between $\sim 1e-4$ and $1e-3$ across chemically different glasses ($P$ = density of states of tunneling two-level systems, $\gamma$ = deformation potential, $\rho$ = mass density, $v$ = sound velocity); equivalently the phonon mean free path is $\sim 150$ wavelengths. Explain this universality, e.g. by interaction-induced renormalization of the defects (Yu and Leggett; Burin and Kagan) or by a generic soft-mode mechanism, and predict where it fails.
Revision 2: Below $\sim 1\,\mathrm{K}$ amorphous solids show specific heat $C \sim T$, thermal conductivity $\kappa \sim T^{2}$ and an internal-friction plateau $Q^{-1} = (\pi/2) C_{\mathrm{tun}}$, with tunneling strength $C_{\mathrm{tun}} = P \gamma^{2}/(\rho v^{2})$ between $\sim 10^{-4}$ and $10^{-3}$ across chemically different glasses ($P$ = density of states of tunneling two-level systems, $\gamma$ = deformation potential, $\rho$ = mass density, $v$ = sound velocity); equivalently the phonon mean free path is $\sim 150$ wavelengths. Explain this universality, e.g. by interaction-induced renormalization of the defects (Yu and Leggett; Burin and Kagan) or by a generic soft-mode mechanism, and predict where it fails.
Settled by · changed · core
Revision 1: A theory deriving $C_{\mathrm{tun}} \sim 1e-4 \text{ to } 1e-3$ from generic properties of glasses, confirmed by a predicted exception or by simulations that compute $P$ and $\gamma$ in several model glasses.
Revision 2: A theory deriving $C_{\mathrm{tun}} \sim 10^{-4} \text{ to } 10^{-3}$ from generic properties of glasses, confirmed by a predicted exception or by simulations that compute $P$ and $\gamma$ in several model glasses.
Kind
phenomenon
Answer type
mechanism
References
(empty)
Literature status
open
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