Spin injection from topological insulator tunnel-coupled to metallic leads

We study theoretically helical edge states of 2D and 3D topological insulators (TI) tunnel-coupled to metal leads and show that their transport properties are strongly affected by contacts as the latter play a role of a heat bath and induce damping and relaxation of electrons in the helical states of TI. A simple structure that produces a pure spin current in the external circuit is proposed. The current and spin current delivered to the external circuit depend on relation between characteristic lengths: damping length due to tunneling, contact length and, in case of 3D TI, mean free path and spin relaxation length caused by momentum scattering. If the damping length due to tunneling is the smallest one, then the electric and spin currents are proportional to the conductance quantum in 2D TI, and to the conductance quantum multiplied by the ratio of the contact width to the Fermi wavelength in 3D TI.     

Luminescent properties of ytterbium-erbium nanostructured lead fluoride silicate glass-ceramics at low temperatures

We have studied the luminescent properties of lead fluoride silicate nanostructured glass-ceramics doped with ytterbium and erbium ions. We have measured luminescence spectra of glass-ceramics in the visible and near-IR ranges at temperatures of 300 and 77 K and under their pumping at a wavelength of 975 nm. We have examined changes in the luminescence spectra of glass-ceramics depending on the time of their secondary thermal treatment, concentration of dopant ions, specimen temperature, and power of excitation radiation.     

Möbius bilipschitz homogeneous arcs on the plane

A möbius bilipschitz mapping is an η-quasimöbius mapping with the linear distortion function η(t) = Kt. We show that if an open Jordan arc γ ? C with distinct endpoints a and b is homogeneous with respect to the family F_K of möbius bilipschitz automorphisms of the sphere C with K specified then γ has bounded turning RT(γ) in the sense of Rickman and, consequently, γ is a quasiconformal image of a rectilinear segment. The homogeneity of γ with respect to F_K means that for all x, y ∈ γ {a, b} there exists f ∈ F_K with f(γ) = γ and f(x) = y. In order to estimate RT(γ) from above, we introduce the condition BR(δ) of bounded rotation of γ, and then the explicit bound depends only on K and δ.     

Spectral luminescence properties of transparent lead fluoride nanoglassceramics doped with erbium ions

Transparent nanoglassceramics has been synthesized based on lead fluoride silicate glass doped with erbium ions. It is shown that heat treatment of lead fluoride silicate glass leads to the formation of nanoscale (16–40 nm) crystalline phase of lead fluoride. X-ray diffraction analysis and measurement of spectral luminescence properties have revealed that the erbium ions enter the crystalline phase of lead fluoride.     

Visualization of the spatio-temporal structure of a pulsed photoelectron beam formed by femtosecond laser radiation

A method based on an original electron microscope created for investigating photoelectron beams is presented. It ensures a nanometer spatial resolution and picosecond time resolution. Electrons appearing when a metal needle is irradiated by femtosecond laser pulses are transmitted through a dielectric microcapillary and are subjected to a ponderomotive potential created by femtosecond laser radiation focused near the capillary tip. The position-sensitive detection scheme allows for the detection of the spatial profile of a photo-electron beam with a magnification of K ≅ 4 × 10⁴. The time structure of the photoelectron beam is visualized by scanning the delay time between laser pulses irradiating the needle and a laser pulse focused near the capillary tip.     

Constructing quasisymmetric functions via graph-directed iterated function systems

Using Tukia’s method for representing a quasisymmetric function as a quasisymmetric sieve, we generalize his modification to the Salem scheme and find a sufficient condition for the collection of functions that realize a structure parametrization of a graph-directed function system of a particular form (a one-dimensional multizipper) to consist of quasisymmetric functions. We give an asymptotically sharp estimate for the quasisymmetry coefficient of these functions in terms of the dilation coefficients of the mappings constituting a given multizipper, which yields a substantially more general method for constructing quasisymmetric functions than Tukia’s construction.     

Modification of Graphene on a Copper Grid during Femtosecond Laser Irradiation: Electron Diffraction and Raman Spectroscopy Studies

The initial stage of a nanosecond discharge in gaps with a high electric field at a cathode is studied by laser methods (interferometric, shadow, schlieren methods). The studies are performed in air at atmospheric pressure. Prominence is given to studying the evolution (appearance and growth) of the plasma channels at an anode and to estimating their parameters.     

Two-band conduction in TiO2

The contribution of electrons and holes to the electrical conduction of titanium dioxide TiO₂ in the Si/TiO₂/Al structure is determined in experiments on the injection of minority carriers from n-type and p-type silicon layers. It is established that both electrons and holes contribute to electrical conduction of the titanium dioxide layer in the Si/TiO₂/Al structure; i.e., the electrical conduction of titanium dioxide has a two-band nature.     

Electronic transport through a contact of a correlated quantum wire with leads of higher dimension

We study theoretically electronic transport through a contact of a quantum wire with 2D or 3D leads and find that if the contact is not smooth and adiabatic then the conduction is strongly suppressed below a threshold voltage V _T , while above V _T the dc current $ \bar I $ \bar I is accompanied by coherent oscillations of frequency f = $ \bar I $ \bar I /e. The effect is related to interelectronic repulsion and interaction of dc current with the Friedel oscillations near a sharp contact. In short conducting channels of length L < L ₀ ≅ ℏV _F /eV _T and at high temperatures T > T ₀ ≅ eV _T /k _B the effect is destroyed by fluctuations.