Nanoscale Physics
Influence of surface anions on the transport of the quasi-one-dimensional surface electrons over helium in the region of scattering by gas

V. A. Nikolaenko, A. V. Smorodin, and S. S. Sokolov
B.Verkin Institute for Low Temperature Physics and Engineering of NAS of Ukraine, Prospekt Nauky, 47, Kharkov - 61103, Ukraine
E-mail: nikolaenko@ilt.kharkov.ua

The behavior of surface electrons in conditions of restricted geometry attracts great attention of physicists. Here presented the results of a preliminary study of the conductivity of quasi-one-dimensional surface electrons (SE) over a helium layer in the presence of surface anions (self-localized electrons, SA).
The linear electron channels were formed over the tops of the profiled substrate consisted of 25 segments of plastic fibers with a diameter of 220 μm covered by a polymer film. The inhomogeneities forming lattice of a wavelike micro-protrusions by step of 5 x 5 μm were on film 70 μm thick. The substrate has been placed on a glass plate of 0.2 mm thick at a height of about 4 mm above the surface of the massive helium. 
It is known that in a dense helium gas the surface electron forms a state of the disk-shaped surface anion having low mobility. According to the experimental and the theoretical data the SE - SA transition depends mainly on both the gas density and the structure and state of the substrate surface [1-4]. The mobility SE in gas region is μg = 8e / (3πħσsng γ) and the mobility for SA is μSA = 2πħα5/2/ (ηm1/2e2Eeff3)  (here e and m is charge and mass electron accordingly ħ is Plank’s constant, σs is the scattering section of electron on helium atom in gas by density ng,  γ-1 is effective Bohr radius of electron, α and η is surface tension and viscosity of liquid helium accordingly).
  
The electron conductivity σ was measured in the temperature range 1.7–3.0 K, where its value is limited by the interaction of electrons with helium atoms in a vapor. Under the monotonic increase in temperature (exponential increase in the density of a vapor phase), the conductivity of SE decreases. However, in present experiments, at T = 2.45 K an abrupt increase of σ is observed (~ 2.5 times). The further increase in T leads to the slowly decrease of σ and then to the substantial its decrease until a transition SE – SA. A fall in conductivity takes place at the higher value of T when the higher is the electron density: ~ 6 • 108 cm-2 (left graph); ~ 109 cm-2 (right graph). The reverse dependence σ (T) is characterized by low conductivity of the system up to temperature 2.45 K. Then there is a growth of σ by approximately an order of magnitude almost to its initial value. 
The observed positive jump of conductivity at T ~ 2.45 K achieves value SE over massive helium. It can be attributed to the topology of the electron configuration on the helium layer in particularly to the specific interaction of the border surface electrons with the surface anions. The motivation for similar research could be in particle the search for quantum dots for a quantum computer. To solving this problem, the further experimental studies are needed. 

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