Unexpected hydrodynamic behavior of multi-electron bubbles in liquid helium I

The authors investigated multi-electron bubbles (with charges Z ∼ 106 electrons) in normal liquid 4He. The drift velocity in an electric field and the charge of the bubbles were measured simultaneously. The drag coefficient was found to be over an order of magnitude higher than expected from ordinary hydrodynamics. The velocities did not show a correlation with the charge and could vary up to a factor of 3 for equally charged bubbles