The Energy Distribution of Two-Level Systems in Various Amorphous Thin Films Measured Using Internal Friction

Amorphous materials are known to universally possess various low-energy excitations generally modeled as two-level systems (TLS) capable of tunneling between states at low temperatures (~1K) and thermal excitation at higher temperatures (>5 K). The measurement and modeling of these states in bulk materials is well represented in the literature, however, relatively few measurements of amorphous thin films have been similarly analyzed. In this presentation, we fit the model of Rau et al. (Phys. Rev. B, 52, 7179, 1995) to the mechanical loss features attributed to TLS in thin films of a-Se, a-Al₂O₃, and others.