Properties of multielectron bubbles in liquid helium

of a bubble (F is the diele~tric onstant of liquid helium) gives the class~cal *'Coulomb radius" of the bubble (this value is accurate for the bubbles considered ( 5 , 6)). For typical charges Z of 10510' electrons, this yields radii between 10 and 100 pm. The electrons in a bubble are confined to a narrow region of only a fcw Bngstrorns width close to the bubble surface, owing to their mutual Coulomb repulsion ( 5 ) , and thus constitute a spherically symmetric two-dimensional Coulomb system with a considerably higher density (10'"electrons/cm2 and more) than in the free-surface case. Thus, the multielectron bubbles might provide information on a regime in the phase diagram of the 2D electron system that has hardly been accessible ta experiments so far. We report here initial experiments with such bubbles, measuring t he~ r charge and concentrating on some dynamical properties like their motion in the liquld helium, oscillations of the bubbles, and their stability. Electrons nn the surface of liquid helium are localized in the direction perpendicular to the surface in a potential well consisting of the image 11otentiaI (plus holding potential) and a potential barrier of l eV duc to the Pauli exclusion principle (see ref. 1 and references cited therein). Because their motion 5.10~-