Spin Transport over Huge Distances in a Magnetized 2D Electron System
Experimental results on the properties of a recently discovered new collective state, the magnetofermionic condensate, are summarized herein. Condensation occurs in a fermionic system, a quantum Hall insulator (filling factor ν = 2), as a result of the formation of a dense ensemble of long-lived spin cyclotron magnetoexcitons, composite bosons. At temperatures below 1 K, the exciton ensemble exhibits a sharp enhancement in its response to an external electromagnetic field due to the formation of a super-absorbing state that interacts coherently with the electromagnetic field. Simultaneously, the electrons below the Fermi level rearrange to form a new non-equilibrium radiative recombination channel. The condensate shows a sharp decrease in viscosity and the ability to spread over macroscopically large distances, on the order of a millimeter, at a speed of ≈103 cm s−1. Due to this rapid long-distance spin transfer, new opportunities in the field of spintronics have been opened up.
The results on the formation of locally strained Ge microstructures on silicon-on-insulator (SOI) substrates and investigation of their optical properties are presented. Suspended Ge structures are formed by optical lithography and plasmachemical and selective chemical etching using the “stress concentration” approach. To provide a heat sink from Ge microstructures, their formation scheme is modified so as to provide the mechanical contact of a part of the suspended microstructure with lower-lying layers. To implement this scheme, SOI substrates with a thin upper Si layer 100 nm in thickness are used. It is shown using the measurements of Raman spectra depending on the pumping power that local heating in such structures decreases. Measurements of the microphotoluminescence spectra show a considerable increase in the signal intensity from strained regions of Ge microstructures as well as the possibility of increasing the maximal optical pumping power (not leading to irreversible changes) for microstructures, in which the mechanical contact of the strained part with lower-lying layers is provided, when compared with suspended structures.
The results of formation of locally stretched Ge microstructures and investigation of their optical properties are presented. Free-hanging Ge structures were obtained by optical lithography, plasma chemical etching and selective chemical etching using the "stress concentration" method. To provide heat dissipation from free-hanging structures, the scheme of their formation was modified so as to provide mechanical contact of the suspended part of the microstructure with the substrate. A significant increase in the intensity of the photoluminescence signal was demonstrated in the stretched regions of These microstructures and the possibility of increasing the maximum optical pumping power (which does not lead to irreversible changes) for microstructures in which the stretched part is mechanically in contact with the substrate, compared with free-hanging structures
New 3-(1H-imidazol-2-yl)-9H-carbazoles and 6,60-di(1H-imidazol-2-yl)-9H,90H-3,30-bicarbazoles have been prepared, starting from 9-ethyl-9H-carbazole-3-carbaldehyde or 9,90-diethyl-9H,90H-[3,30-bicarbazole]-6,60-dicarbaldehyde through their reactions with 4-methoxyaniline or 4-fluoroaniline, benzil or 2,20-thenil [1,2-di(thien-2,20-yl) glyoxal] and ammonium acetate on reflux in glacial acetic acid. The obtained compounds have been shown to demonstrate an effective fluorescence in the blue spectral region, exhibiting quantum yields in the range of 0.08e0.51, depending on their molecular structure and solvent polarity. The nature of the observed absorption spectra has been elucidated by the TDDFT calculations.
Electron spin relaxation in a spin-polarized quantum Hall state is studied. Long spin-relaxation times that are at least an order of magnitude longer than those measured in previous experiments were observed and explained within the spin-exciton relaxation formalism. The absence of any dependence of the spin-relaxation time on the electron temperature and on the spin-exciton density, and a specific dependence on the magnetic field indicate a definite relaxation mechanism—spin-exciton annihilation mediated by spin-orbit coupling and a smooth random potential.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.