The rotation anomaly of high quality $^{4}$He single crystals

We have built a transparent torsional oscillator in order to monitor the growth of $^{4}$He crystals near 20 mK. It allows us to measure the rotational inertia of high quality oriented single crystals and compare it with low quality crystals or polycrystals grown at constant volume. It is also possible to vary the $^{3}$He concentration from 0 to 0.3 ppm (natural purity). Since the change in TO period associated with the change in shear modulus of the He sample could be calculated, we could see if supersolidity is really due to superflow along dislocation lines.