Why phonon scattering in glasses is universally small at low temperatures
Abstract
We present a novel view of the standard model of tunneling two level systems (TLS) to explain the puzzling universal value of a quantity, C 3× 10-4, that characterizes phonon scattering in glasses below 1 K as reflected in thermal conductivity, ultrasonic attenuation, internal friction, and the change in sound velocity. Physical considerations lead to a broad distribution of phonon-TLS couplings that (1) exponentially renormalize tunneling matrix elements, and (2) reduce the TLS density of states through TLS-TLS interactions. We find good agreement between theory and experiment for a variety of individual glasses.
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