Charge complexes in helium films
Abstract
The effects of the interaction of positive ions with surface electrons (SE) in a superfluid helium film are theoretically investigated. The possibility of using the Coulomb crystallization of positive ions to produce a surface-electron band spectrum is investigated. It is shown that the electron-ion coupling is weak (i.e., the bands are broad) in the case of high positive-ion concentrations and strong (i.e., the bands are narrow) in the case of low concentrations. The dynamics of the dipolar crystal in a helium film is investigated in the strong-coupling limit and in the case when the number of electrons is equal to the number of ions, and the melting point of the crystal is determined. The surface-excitation spectrum of a helium film electrified by dipolar quasiparticles is computed. It is shown that the stability of the film strongly depends on the phase state (liquid or crystalline) of the dipolar system. The possibility of the existence of complex charge lattices in a helium film with concentrations of positive and negative charges that are multiples of each other are analyzed.