Electron Self-Trapping in Vortex Rings in Superfluid Helium

Abstract

The mobility of electrons injected in the majority of nonpolar dielectric liquids is a few orders of magnitude higher than the mobility of positive ions. However, the behavior of electrons in liquid helium is anomalous. The electron mobility is a few orders of magnitude lower than the value expected according to the classical Langevin theory and even a few times lower than the mobility of positive ions. The reason is that it is energetically favorable for an electron to be localized in nanobubble owing to a strong exchange repulsion from helium atoms. In addition to ordinary electron bubbles, two more types of negative charge carriers were discovered many years ago in superfluid helium: “fast” and “exotic” ions. The mobility of fast ions is approximately seven times higher than the mobility of electron bubbles, whereas the mobility of a family of exotic ions (more than ten members) lies between these two values. In the present work a model according to which fast and exotic negative ions in superfluid helium represent the localized states of electrons in vortex rings is presented. The quantization of radial and longitudinal motions of electrons inside the vortex core and the quantization of the vortex motion of liquid helium around the charged complex lead to the existence of a whole family of excited states of electron vortices with different radii and quanta of vorticity. The proposed simple model of autolocalization of injected electrons in vortex rings allows to understand the nature of fast and exotic ions in superfluid helium.