High-temperature electron localization in dense He gas

Abstract

We report accurate measurements of the mobility of excess electrons in high-density helium gas in extended ranges of temperature [(26 < or = T < or = 77) K] and density [(0.05 < or = N < or = 10.0) atoms nm(-3)]. The aim is the investigation of the combined effect of temperature and density on the formation and dynamics of localized electron states. The main result of the experiment is that the formation of localized states essentially depends on the relative balance of fluid dilation energy, repulsive electron-atom interaction energy, and thermal energy. As a consequence, the onset of localization depends on the medium disorder through gas temperature and density. The transition from delocalized to localized states shifts to larger densities as temperature is increased. This behavior can be understood in terms of a simple model of electron self-trapping in a spherically symmetric square well.

Electron mobility in liquid and supercritical helium measured using corona discharges: a new semi-empirical model for cavity formation

“…Low temperatures assist the localisation process which is reflected by a shift in the mobility transition region to higher densities with increasing temperature. 5 Cavity formation around electrons in LHe has been studied extensively using various methods 12,13 including density function theory (DFT). [14][15][16][17] DFT methods specially developed for LHe provide good agreement with first principles methods for small helium clusters, 18 but have the disadvantage that they are restricted to zero Kelvin.…”

Electron and ion transport in dense rare gases

“…Ne [14]] and He [9,15] show a further dramatic decrease of the mobility at high density until µ 0 N levels off at very small values, as shown in Figure 2. This drop is commonly associated to self-trapping of electrons in (partially) empty cavities, known as bubbles [16], endowed with very small hydrodynamic mobility, whose existence has been reported for the first time in superfluid He [17].…”

“…In Figure 2 experimental results obtained for the zero-field densitynormalized mobility µ 0 N in He, Ne, Ar, and Xe are shown [8,9,10,13,14]. Constant lines in the picture indicate the predictions of kinetic theory that are strongly violated in real experiments.…”

“…In this way, the temperature T is not density N for He (squares) [9], Ne (triangles) [10], Ar (closed dots) [11,12], Xe (open dots) [13]. The constant lines are the prediction of kinetic theory.…”

“…Whereas the mobility measurements in He [9], Ne [14,10], and Ar [11,12] have been carried out along isotherms, the Xe results have been obtained at saturated vapor pressure [13]. In this way, the temperature T is not density N for He (squares) [9], Ne (triangles) [10], Ar (closed dots) [11,12], Xe (open dots) [13].…”