From classical mobility to hopping conductivity: charge hopping in an ultracold gas

This paper explore the interactions between ions and their neutral parent atoms in the ultralow energy regime. It is shown that the large charge transfer cross section at low temperatures together with the spread of atom and ion thermal de Broglie waves allow electrons to hop from atoms to ions. At such low temperatures, atoms and ions are moving extremely slowly (the gas is essentially frozen), and electron hopping provides an efficient charge diffusion through the neutral gas. The system becomes effectively conducting: this is analogous to hopping conductivity in doped semiconducting materials, where electrons hop from impurity atoms.