Spin relaxation and combined resonance in two-dimensional electron systems with spin-orbit disorder

Disorder in spin-orbit (SO) coupling is an important feature of real low-dimensional electron structures. We study spin relaxation due to such a disorder as well as resulting abilities of spin manipulation. The spin relaxation reveals quantum effects when the spatial scale of the randomness is smaller than the electron wavelength. Due to the disorder in SO coupling, a time-dependent external electric field generates a spatially random spin-dependent perturbation. The resulting electric dipole spin resonance in a two-dimensional electron gas leads to spin injection in a frequency range of the order of the Fermi energy. These effects can be important for possible applications in spintronics.Comment: 4 pages, 3 figure

Spin dephasing and pumping in graphene due to random spin-orbit interaction

We consider spin effects related to the random spin-orbit interaction in graphene. Such a random interaction can result from the presence of ripples and/or other inhomogeneities at the graphene surface. We show that the random spin-orbit interaction generally reduces the spin dephasing (relaxation) time, even if the interaction vanishes on average. Moreover, the random spin-orbit coupling also allows for spin manipulation with an external electric field. Due to the spin-flip interband as well as intraband optical transitions, the spin density can be effectively generated by periodic electric field in a relatively broad range of frequencies.Comment: 9 pages, 7 figure

Robust to impurity-scattering spin Hall effect in two-dimensional electron gas

We propose a mechanism of spin Hall effect in two-dimensional electron gas with spatially random Rashba spin-orbit interaction. The calculations based on the Kubo formalism and kinetic equation show that in contrast to the constant spin-orbit coupling, spin Hall conductivity in the random spin-orbit field is not totally suppressed by the potential impurity scattering. Even if the regular contribution is removed by the vertex corrections, the terms we consider, remain. Therefore, the intrinsic spin-Hall effect exists being, however, non-universal.Comment: 4+ pages, 2 figure

Surface hardening of stainless steel by runaway electronspreionized diffuse discharge in air atmosphere

In this paper we present microhardness measurements of stainless steel surface treated by diffuse discharge in air atmosphere. The cleaning from carbon in comparison to the initial sample was observed at a depth exceeding 20 nm. The oxygen concentration was also increased in comparison to that in the initial sample at a depth of up to about 50 nm. Comparative analysis shows that after treatment the microhardness of stainless steel surface increased in 2 times due to interaction of near-surface layers with product of plasma chemical reactions produced in diffuse discharge

Pure spin photocurrents in low-dimensional structures

As is well known the absorption of circularly polarized light in semiconductors results in optical orientation of electron spins and helicity-dependent electric photocurrent, and the absorption of linearly polarized light is accompanied by optical alignment of electron momenta. Here we show that the absorption of unpolarized light leads to generation of a pure spin current, although both the average electron spin and electric current vanish. We demonstrate this for direct interband and intersubband as well as indirect intraband (Drude-like) optical transitions in semiconductor quantum wells (QWs).Comment: 4 pages, 3 figure

Cyclotron Resonance Assisted Photocurrents in Surface States of a 3D Topological Insulator Based on a Strained High Mobility HgTe Film

We report on the observation of cyclotron resonance induced photocurrents, excited by continuous wave terahertz radiation, in a 3D topological insulator (TI) based on an 80 nm strained HgTe film. The analysis of the photocurrent formation is supported by complimentary measurements of magneto-transport and radiation transmission. We demonstrate that the photocurrent is generated in the topologically protected surface states. Studying the resonance response in a gated sample we examined the behavior of the photocurrent, which enables us to extract the mobility and the cyclotron mass as a function of the Fermi energy. For high gate voltages we also detected cyclotron resonance (CR) of bulk carriers, with a mass about two times larger than that obtained for the surface states. The origin of the CR assisted photocurrent is discussed in terms of asymmetric scattering of TI surface carriers in the momentum space. Furthermore, we show that studying the photocurrent in gated samples provides a sensitive method to probe the effective masses and the mobility of 2D Dirac surface states, when the Fermi level lies in the bulk energy gap or even in the conduction band

Spin relaxation of conduction electrons in (110)-grown quantum wells

The theory of spin relaxation of conduction electrons is developed for zinc-blende-type quantum wells grown on (110)-oriented substrate. It is shown that, in asymmetric structures, the relaxation of electron spin initially oriented along the growth direction is characterized by two different lifetimes and leads to the appearance of an in-plane spin component. The magnitude and sign of the in-plane component are determined by the structure inversion asymmetry of the quantum well and can be tuned by the gate voltage. In an external magnetic field, the interplay of cyclotron motion of carriers and the Larmor precession of electron spin can result in a nonmonotonic dependence of the spin density on the magnetic field.Comment: 5 pages, 3 figure

Особенности IPO как инвестиционного инструмента производственного предприятия

У статті розглянуто особливості проведення публічного розміщення акцій (IPO) виробничими підприємствами, законодавчий механізм проведення IPO в Україні. Особливу увагу приділено дослідженню переваг проведення первинного публічного розміщення акцій в Україні та за її межами. Досліджено стримуючі фактори розвитку ринку IPO, виявлення яких дозволить підвищити інтерес вітчизняних компаній до розвитку цього напрямку інвестиційної діяльності.The article discusses the features of the public offering (IPO) production enterprises, the legislative mechanism of the IPO in Ukraine. Particular attention is paid to research the benefits of the IPO in Ukraine and abroad. Studied constraints of market development IPO, which will improve the detection of interest in domestic companies to develop this area of investment activity.В статье рассмотрены особенности проведения публичного размещения акций (IPO) производственными предприятиями, законодательный механизм проведения IPO в Украине. Особое внимание уделено исследованию преимуществ первичного публичного размещения акций в Украине и за ее пределами. Исследованы сдерживающие факторы развития рынка IPO, выявление которых позволит повысить интерес отечественных компаний в этом направлении инвестиционной деятельности

Excitonic absorption and emission in diamond near the edge of fundamental absorption

The study of optical absorption of CVD diamond near the fundamental absorption edge was performed in the temperature range of 87-296 K. At temperatures lower than 195 K the absorption was practically constant. At higher temperatures the sharp increase of absorption took place. This sharp increase was attributed to the sharp enrichment of the phonon spectrum. Same phonon modes have different contributions to the negative and the positive branches of freeexciton absorption. For the negative branch (phonon absorption) the TA-mode dominated. For the positive branch (phonon emission) the TO-mode dominated. The possibility of diamond-based cathodoluminescent UV-sources at 235 nm was demonstrated

Bloch-Redfield theory of high-temperature magnetic fluctuations in interacting spin systems

We study magnetic fluctuations in a system of interacting spins on a lattice at high temperatures and in the presence of a spatially varying magnetic field. Starting from a microscopic Hamiltonian we derive effective equations of motion for the spins and solve these equations self-consistently. We find that the spin fluctuations can be described by an effective diffusion equation with a diffusion coefficient which strongly depends on the ratio of the magnetic field gradient to the strength of spin-spin interactions. We also extend our studies to account for external noise and find that the relaxation times and the diffusion coefficient are mutually dependent