Observation of Cavitation on Electron Bubbles at Small Negative Pressures

Acoustic cavitation is a powerful technique to probe electron bubbles inside the liquid helium. The critical pressure to explode a bubble depends on the number and quantum state of electrons inside the bubble and if the bubble is trapped on a vortex. Here, we report cavitation events that occur at pressure magnitudes approximately 70% lower compared to single electron bubbles. We have considered various possibilities, e.g., single electron bubbles trapped on vortex lines or primary electrons depositing the energy at the acoustic focus and compared the results of our experiments with past measurements reported in the literature. We consider the possibility these new species of bubbles are multielectron bubbles with a small (< 20) number of electrons and discuss future experiments to confirm the same.