Decoupling between propagating acoustic waves and two-level systems in hydrogenated amorphous silicon

Specific heat measurements of hydrogenated amorphous silicon prepared by hot-wire chemical vapor deposition show a large density of two-level systems at low temperature. Annealing at 200 degrees C, well below the growth temperature, does not significantly affect the already-low internal friction or the sound velocity, but irreversibly reduces the non-Debye specific heat by an order of magnitude at 2 K, indicating a large reduction in the density of two-level systems. Comparison of the specific heat with the internal friction suggests that the two-level systems are uncharacteristically decoupled from acoustic waves, both before and after annealing. Analysis yields an anomalously low value of the coupling constant, which increases upon annealing but still remains anomalously low. The results suggest that the coupling constant value is lowered by the presence of hydrogen.

Automated summary

Specific heat measurements of hydrogenated amorphous silicon prepared by hot-wire chemical vapor deposition reveal a large density of two-level systems at low temperature. Annealing at 200 degrees C irreversibly reduces the non-Debye specific heat by an order of magnitude at 2 K, indicating a significant reduction in the density of two-level systems. The presence of hydrogen is suggested to anomalously lower the coupling constant value.