Study of the Properties of an Excess Electron in Liquid Helium. I. The Nature of the Electronmdash;Helium Interactions

摘要

In this paper we present a theoretical study of the free and localized states of an excess electron in liquid helium. Electronmdash;helium interactions are treated by the pseudopotential method, while multiple scattering effects on the properties of a quasifree electron in the dense fluid are treated using the Wignermdash;Seitz model. It is demonstrated that the planehyphen;wave state is not the lowest energy state for an excess electron in liquid helium and that fluid deformation leads to a localized state of lower energy. The large, repulsive heliumhyphen;atom pseudopotential coupled with the small helium polarization potential lead to electron localization which may be attributed entirely to shorthyphen;range repulsions. The following experimental observations are adequately interpreted by these results: (a) The energy barrier of liquid helium for electrons, (b) the densityhyphen;dependent transition from a delocalized state to a localized state of the excess electron, (c) the mobility of an excess electron in normal4He and in3He. Pressure and temperature effects on the electron bubble are also discussed. It is concluded that a pressurehyphen;induced transition from the localized to the delocalized state of the excess electron will not occur in the fluid domain even at high pressures. Finally, we present some speculations concerning the optical properties of the excesshyphen;electron center.