Tunneling from Electronic Bubble States in Liquid Helium Through the Liquid-Vapor Interface

Abstract

Ions have been extensively used in liquid helium to study both the superfluid and normal states. If the experimental cell is only partially filled with liquid, then the ions must pass through the phase boundary between liquid and vapor in order to reach a collector located in the vapor. The transport of charges across a phase boundary is of general interest in a variety of biological, chemical, and physical problems, helium being presumably one of the simplest cases. It has been observed that positive ions are unable to penetrate the liquid-vapor interface. However, negative ions (electronic bubbles) pass into the vapor quite easily, providing the temperature is not too low (T > 2° K). As the temperature is lowered, negative ions experience a rapidly increasing difficulty in penetrating the free surface, resulting in a vanishing current at moderate electric fields below 1°K.