Atomistic simulations of mechanical loss in amorphous silicon

Brownian noise from the mirror coatings in current gravitational wave detectors serves as one of the predominant limiting factors in detecting gravitational wave events [1]. Projected reductions in Brownian noise through the lowering of operational temperatures prove to be insufficient for future sensitivity targets and necessitates the search for alternative candidates. To gain insight into the atomistic mechanisms of internal friction, we explore the potential energy landscape of amorphous silicon, a paradigmatic amorphous coating material, with molecular simulations. Structural transitions in the form of two-level systems (TLS) are identified, and the distributions of relevant TLS parameters (barriers, asymmetry, attempt frequencies) are obtained and compared with other amorphous coating materials. A calculation of mechanical dissipation in the 10-1000 Hz regime is performed via harmonic transition state theory and discussed in the experimental context.

[1] J. Steinlechner, Phil. Trans. R. Soc. A. 376: 20170282 (2018)