Internal mechanical dissipation mechanisms in amorphous silicon

TL;DR

This study identifies and characterizes two main types of two-level systems in amorphous silicon, revealing their dependence on preparation methods and quantifying their contribution to mechanical loss relevant for quantum and gravitational wave applications.

Contribution

The paper introduces a detailed computational analysis of TLSs in amorphous silicon, linking their types to specific atomic mechanisms and quantifying their impact on mechanical dissipation.

Findings

Majority of TLSs are bond-defect hopping and bond exchange mechanisms.

Mechanical loss angle is approximately 0.001 at room temperature.

Loss angle decreases to about 0.0001 at 150 K.

Abstract

Using the Activation-Relaxation Technique-nouveau, we search for two-level systems (TLSs) in models of amorphous silicon (a-Si). The TLSs are mechanisms related to internal mechanical dissipation and represent the main source of noise in the most sensitive frequency range of the largest gravitational wave detectors as well as one of the main sources of decoherence in many quantum computers. We show that in a-Si, the majority of the TLSs of interest fall into two main categories: bond-defect hopping where neighbors exchange a topological defect and the Wooten-Winer-Weaire bond exchange. The distribution of these categories depends heavily on the preparation schedule of the a-Si. We use our results to compute the mechanical loss in amorphous silicon, leading to a loss angle of 0.001 at room temperature, decreasing to 0.0001 at 150 K in some configurations. Our modeling results indicate that multiple classes of events can cause experimentally-relevant TLSs in disordered materials and, therefore, multiple attenuation strategies might be needed to reduce their impact.