Dissipation in metallic nano-mechanical resonators at millikelvin temperatures.

A magneto-motive detection scheme has often been employed to study dissipation in semiconducting nano-mechanical resonators at millikelvin temperatures. This scheme involves placing the beam in a large applied magnetic field and driving the mechanical resonance by sending rf currents through a thin metal electrode plated on the beam. The motion is then detected by measuring the induced e.m.f in the electrode. As a first step in understanding possible damping effects due to metallic films, we have fabricated free standing metallic resonators. We have fabricated doubly clamped beams out of $Au$ and $Au/Pd$ alloys (dimensions length $3-5 \mu m $ ,thickness $\approx 50nm$ and width $\approx 200 nm $). Beams of this dimension have a resonant frequency around $5-10$ MHz. We will report measurements, performed in a dilution refrigerator,of the quality factor $Q$ in these resonators as a function of temperature and magnetic field (up to 15 T).