Excitation and Detection of Surface Waves on Normal and Superfluid 3He
We describe the measurement principles to excite and detect surface waves on liquid helium at very low temperatures. We excited the waves mechanically by rocking the whole cryostat with frequencies of few hertz. The waves were detected capacitively with an interdigital capacitor on a vertical wall of the cuboid experimental volume. In superfluid 3He at around 0.2 mK at least eleven surface resonances were observed below 11 Hz whereas in normal fluid only a few resonances were observable above 50 mK.
KeywordsSurface waves Interdigital capacitor Superfluid helium-3
We thank A.J. Niskanen for microfabrication of the interdigital capacitors, and V.B. Eltsov, P.J. Heikkinen, J.J. Hosio, A.Ya. Parshin, A. Salmela, A. Sebedash and V. Tsepelin for valuable discussions. This work has been supported in part by the EU 7th Framework Programme (FP7/2007-2013, Grant No. 228464 Microkelvin) and by the Academy of Finland though its LTQ CoE grant (project no. 250280). We also acknowledge the grants from Jenny and Antti Wihuri Foundation, and the National Doctoral Programme in Materials Physics.