Evidence of universality in the dynamical response of nanomechanical ultra-nanocrystalline diamond resonators at millikelvin temperatures

We report millikelvin-temperature measurements of dissipation and frequency shift in megahertzrange resonators fabricated from ultra-nanocrystalline diamond. Frequency shift δf/f0 and dissipation Q−1 demonstrate temperature dependence in the millikelvin range similar to the glass model of two level systems. The logarithmic temperature dependence of δf/f0 is in good agreement with the glass model, where phonon relaxation and phonon resonant absorption is observed. Dissipation shows a weak power law, Q−1 ∝ T 1 3 , followed by saturation at low temperature. A comparison of both the frequency shift and dissipation in equivalent nanomechanical structures made of singlecrystal silicon and gallium arsenide indicates universality in the dynamical response.