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Wong, Daniel Ka Sing

University of British Columbia

At around the 100 Hz regime, thermal noise within the amorphous mirror coatings of current gravitational wave detectors starts to become a predominant source of noise in the interferometer setup. Due to intrinsic mechanical loss of the current coating materials, lowering the operational temperature of the detector is unable to sufficiently reduce the thermal noise for future iterations of gravitational wave detectors running at cryogenic temperatures. Given the difficulty in reducing this thermal noise, there is an incentive to investigate alternative materials that may replace the current mirror coatings. This work serves as a primary investigation into amorphous silicon, which is a candidate to replace current coating materials, using atomistic simulations. Through the theory of dissipation in two-level systems and the characterization of the potential energy landscape as a collection of two-level systems, a calculation of mechanical loss can be performed. Molecular dynamics and other computational techniques are utilized to identify and parameterize these two-level systems in computationally generated amorphous silicon samples. Using the two-level system parameters, the first calculation of mechanical loss of amorphous silicon at low temperatures in the 100 Hz regime is obtained. This study finds that only a small percentage of two-level systems contribute significantly to the total mechanical loss of the system. Furthermore, these important two-level systems are found to have low energy asymmetry, with their average energy barrier controlling the temperature at which the two-level system contributes to the mechanical loss. Finally, this study provides a microscopic description of the atomic motions responsible for the transition between states within two-level systems. Each two-level system is generally found to fall within one of three different classifications of atomic motion.

Text

2022-09-29

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82783

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/