Lifetime of surface-state electrons on liquidHe4. II. Electron lattice

Abstract

Electrons trapped by their image potential on the surface of liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ can escape into the gas by thermal ionization. I have calculated the rate of ionization, assuming that the electron motion parallel to the liquid surface is described by the collective motion of an electron crystal. The first electrons to leave the surface extract their ionization energy from the kinetic energy of those that remain behind. This adiabatic cooling effect rapidly lowers the electron temperature to a small fraction of the liquid temperature. The ionization rate is substantially less for this electron-crystal model than for the free-electron model of the electron motion parallel to the surface. The rate also depends on the density of surface electrons.