Alkali-metal-induced Fermi level and two dimensional electrons at cleaved InAs(110) surfaces

Low-temperature Hall measurements have been performed on two-dimensional electron gases (2DEGs) induced by deposition of Cs or Na on in situ cleaved surfaces of p-type InAs. The surface donor level, at which the Fermi energy of the 2DEG is pinned, is calculated from the observed saturation surface electron density using a surface potential determined self-consistently. The results are compared to those of previous photoelectron spectroscopy measurements.Comment: 3 pages, 4 figure

Magnon topological transition in skyrmion crystal

We study the magnon spectrum in skyrmion crystal formed in thin ferromagnetic films with Dzyalosinskii-Moria interaction in presence of magnetic field. Focusing on two low-lying observable magnon modes and employing stereographic projection method, we develop a theory demonstrating a topological transition in the spectrum. Upon the increase of magnetic field, the gap between two magnon bands closes, with the ensuing change in the topological character of both bands. This phenomenon of gap closing, if confirmed in magnetic resonance experiments, may deserve further investigation by thermal Hall conductivity experiments.Comment: 6 pages, 4 figure

Effective Hamiltonian of topologically protected qubit in a helical crystal

We study a superlattice formed by tunnel-coupled identical antidots periodically situated in a two-dimensional topological insulator placed in a magnetic field. The superlattice spectrum can be controlled by gate electrodes or by changing the magnetic flux through the antidots. We demonstrate that a topologically protected qubit appears at the boundary between two regions with different fluxes. The qubit properties depend on the value of the flux jump on the boundary and can be controlled by the gate voltage. We derive the effective Hamiltonian of such a qubit and analyze the dependence of its properties on the main parameters of the superlattice: the tunnel coupling between antidots, and the probability of jumps with the spin flip.Comment: 8 pages, 2 figure

Controllable Synthesis of Few-Layer Graphene on β-SiC(001)

Few-layer graphene exhibits exceptional properties that are of interest for fundamental research and technological applications. Nanostructured graphene with self-aligned domain boundaries and ripples is one of very promising materials because the boundaries can reflect electrons in a wide range of energies and host spin-polarized electronic states. In this chapter, we discuss the ultra-high vacuum synthesis of few-layer graphene on the technologically relevant semiconducting β-SiC/Si(001) wafers. Recent experimental results demonstrate the possibility of controlling the preferential domain boundary direction and the number of graphene layers in the few-layer graphene synthesized on the β-SiC/Si(001) substrates. Both these goals can be achieved utilizing vicinal silicon wafers with small miscuts from the (001) plane. This development may lead to fabricating new tunable electronic nanostructures made from graphene on β-SiC, opening up opportunities for new applications

Steady operation of the electric drive of pipeline armature in the emergency situation at low ambient temperatures

This scientific work is devoted to the study of the electric drive operation of pipeline armature at low ambient temperatures. Hit of moisture into reducer and rare inclusions in operation of locking regulator are led to curdling lubricant that causes the increased wear of mechanical knots. There is a probability of freezing mechanical components; it leads to emergency situations. The problem of improving working efficiency of the electric drive of shut-off regulating armature at low ambient temperatures of the environment is solved in this work. A simulation model of the GUSAR electric drive was developed to solve this problem. Studies of the simulation model show the need to limit the torque increase rate on a drive motor shaft. The algorithm of setting of PI speed controller to obtain acceptable transient processes is suggested. Recommendations for the use of the algorithm in the microprocessor control system of electric drive are proposed. It is shown that the electric drive operation algorithm with torque increasing limitation on the motor shaft will be smoothly working off the perturbing actions that occur in pipeline armature

Atomic and electronic structure of nanostructured few-layer graphene with self-aligned boundaries synthesized on SiC/Si(001) wafers

This work was partially supported by the Russian Academy of Sciences, Russian Foundation for Basic Research (grant № 17-02-01139, 17-02-01291), Beijing Institute of Technology Research Fund Program for Young Scholars, and Science Foundation Ireland