Low-temperature anomalies in the dissipation of small mechanical resonators

At very low temperatures the dissipation of a mechanical resonator is normally expected to be featureless and to vary slowly with temperature. Here we report measurements made at low-mK temperatures using a simple single-crystal silicon beam with a smallest dimension of 2.5 $\mu{\rm m}$. Contrary to results obtained on larger resonators these data show a series of dissipation peaks which grow in magnitude with decreasing temperature. One sample exhibited five distinct peaks with equal spacings of 7.7 mK