Proximity phenomena in cold gas of multicharged atoms (Review Article)
LIONS, NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay 91191 Gif sur Yvette Cedex, France
nstitute of Solid State Physics RAS, Chernogolovka, Moscow District, 2 Academician Ossipyan str., 142432 Russia
Received March 16, 2016
The possible proximity effects in the cold multi-charged gas atoms are considered. The rarefied gas density nd of heavy atoms (Z >> 1) at low temperatures in the framework of well-known Thomas–Fermi (TF) approximation giving an opportunity to study the statistical properties of a single atom is studied. To preserve the advantages of the TF formalism, success-fully used in a spherically symmetric problems, the external boundary conditions (taking into account the finiteness of the density of the donors nd ≠ 0 are also symmetrized and are written in the standard manner. We are using the spherical Wigner–Seitz cell model, preserving the full charge inside the cell. This model shows that at zero temperature in a rar-efied gas of such atoms there is an effective long-range interaction proxi Eproxi (nd). The sign Eproxi depends on the properties of the outer shell of a single atom. The long-range degree of Eproxi interaction properties is estimated by comparison with the known London dispersion forces of attraction ELond (nd) < 0, considered as a long-range. For the noble gases argon, krypton, xenon Eproxi > 0, for alkali and alkaline earth atoms Eproxi < 0. At finite temperatures TF statistics reveals abnormally large proximity effect, reflecting the evaporation of electrons localized by Coulomb centers to the continuous spectrum (so-called electron thermal dissociation). This phenomenon is self-consistently described by theory TF theory via the dependence Eproxi on temperature. The value of Eproxi corresponds to the correlation energy in a gas of interacting particles. A comparison of the TF formalism results with well-known statements of the correlation theory of classical plasma is provided. Some possibilities to verify this formalism experimentally are also discussed. The metal–vacuum boundary in a Casimir cell (small vacuum gap between semi-infinite conductive media of a different nature) is one of exampels. In this equilibrium system electrons may extend beyond the ion background to the 2l area with a probability depending on electron cloud interactions Eproxi inside the conductive plates of a Casimir cell. In semiconductors the role of Casimir cell play different types of multilayer heterostructures (quantum wells). The thermal component of proximity effects in these devices provides insight of /represents? the main properties of the dissociation process in doped semi-conductors. In particular, the positivity of Eproxi > 0 means that the TF donors of finite density (nd ≠ 0) forme in semiconductor some degenerate semiconducting state: there is a finite density of free carriers at zero temperature. This density increases, according to a power law with temperature increase.
PACS: 71.10.–w Theories and models of many-electron systems; PACS: 73.21.–b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems.