Phonon Absorption Due to Two-Level Systems in Metallic Glasses
Phonons in metallic glasses at low temperatures are scattered by two-level systems (TLS) arising from atomic tunnelling states [1, 2]. The TLS themselves are heavily damped by inelastic scattering of conduction electrons [1,2], and phonon absorption by these TLS cannot realistically be treated using elementary perturbation theory. A more sophisticated theory has been developed  to describe resonant phonon scattering by heavily damped TLS and this is extended here to include relaxation absorption.
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