Electrically excited size and shape oscillations of bubbles in liquid helium-4*

Electrons on the surface of liquid helium form a defect-free 2D electron system (2DES). Multielectron bubbles (MEBs) are cavities in liquid helium with a large number of electrons pushed against the inner surface of the bubbles, and they provide a platform to study this system of interacting electrons on curved surfaces and at high charge densities. The coupling of electrons with the surface of an MEB can be probed by observing the size and shape fluctuations of the MEBs, which in turn can be excited using electrical fields. In our experiments, the MEBs were attached to a dielectric surface. Electrical excitation of various frequencies was used to excite and identify the various normal modes of the bubbles. The experimental resonant frequencies were found to be slightly higher than the theoretical predictions for a bubble in bulk, and this difference is further investigated computationally. We believe understanding the resonance and dissipation of the surface modes can lead to a better understanding of the behavior of 2DES in MEBs.