Spin orientation by electric current in (110) quantum wells

We develop a theory of spin orientation by electric current in (110)-grown semiconductor quantum wells. The controversy in the factor of two from two existed approaches is resolved by pointing out the importance of energy relaxation in this problem. The limiting cases of fast and slow energy relaxation relative to spin relaxation are considered for asymmetric (110) quantum wells. For symmetricly-doped structures the effect of spin orientation is shown to exist due to spatial fluctuations of the Rashba spin-orbit splitting. We demonstrate that the spin orientation depends strongly on the correlation length of these fluctuations as well as on the ratio of the energy and spin relaxation rates. The time-resolved kinetics of spin polarization by electric current is also governed by the correlation length being not purely exponential at slow energy relaxation. Electrical spin orientation in two-dimensional topological insulators is calculated and compared with the spin polarization induced by the magnetic field.Comment: 8 pages, 2 figure

Band shape determination with robust estimator based on continuous wavelet transform

The paper focuses on an alternative approach that allows one to identify overlapping band shapes with the help of the continuous wavelet transform (CWT). We show that less number of special points for determining a band shape is required unlike the fractional derivative spectrometry method [S.S. Kharintsev, M.Kh. Salakhov, Spectrochim. Acta Part A, 60 (2004) 2125]. Besides, the CWT-based derivative spectrometry can be successfully utilized in a case of complex spectra corrupted with a white and/or high-frequency noise. The power of this method is illustrated on model examples and experimental spectra of 1,2-diphenylethane in crystalline and melted phase. © 2005 Elsevier B.V. All rights reserved

Modeling the UO2 reduction process

Methods of molecular dynamics and DFT calculations have been used to study the reduction mechanisms of UO2 as the most representative part of spent nuclear fuel to metallic uranium. It is shown that the critical softening of the combined modulus of elasticity C11-C12 to zero is the reason for the destruction of the UO2 crystal as a result of the removal of oxygen from it. This destruction is accompanied by an order-disorder phase transition in the oxygen subsystem of the crystal under consideration. DFT calculations indicate a continuous decrease in the band gap as oxygen is removed from the UO2 crystal. When the system reaches the composition U2O3, the band gap disappears and the system becomes electrically conductive. The appearance of the dielectric-conductor transition explains the realization of the FFC Cambridge process during the recovery of spent nuclear fuel. The passage of Li+ and Cl– ions of the LiCl melt through cylindrical channels in a UO2 crystal with cross-sectional radii from 0.25 up to 2 nm has been studied. The strength of the external electric field required for the passage of these channels decreases with an increase in the channel cross section, and the number of Cl– ions entering the channel increases. On the walls of the channels that pass ions with charges of both signs, colonies of adsorbed Cl– and Li+ atoms appear separated from each other, between which strong electric fields are formed. The existence of such fields can cause Li+ ions to move deep into the material being reduced.https://doi.org/10.15826/elmattech.2023.2.01

Steady-state spin densities and currents

This article reviews steady-state spin densities and spin currents in materials with strong spin-orbit interactions. These phenomena are intimately related to spin precession due to spin-orbit coupling which has no equivalent in the steady state of charge distributions. The focus will be initially on effects originating from the band structure. In this case spin densities arise in an electric field because a component of each spin is conserved during precession. Spin currents arise because a component of each spin is continually precessing. These two phenomena are due to independent contributions to the steady-state density matrix, and scattering between the conserved and precessing spin distributions has important consequences for spin dynamics and spin-related effects in general. In the latter part of the article extrinsic effects such as skew scattering and side jump will be discussed, and it will be shown that these effects are also modified considerably by spin precession. Theoretical and experimental progress in all areas will be reviewed

Rational solutions of the discrete time Toda lattice and the alternate discrete Painleve II equation

The Yablonskii-Vorob'ev polynomials $y_{n}(t)$, which are defined by a second order bilinear differential-difference equation, provide rational solutions of the Toda lattice. They are also polynomial tau-functions for the rational solutions of the second Painlev\'{e} equation ($P_{II}$). Here we define two-variable polynomials $Y_{n}(t,h)$ on a lattice with spacing $h$, by considering rational solutions of the discrete time Toda lattice as introduced by Suris. These polynomials are shown to have many properties that are analogous to those of the Yablonskii-Vorob'ev polynomials, to which they reduce when $h=0$. They also provide rational solutions for a particular discretisation of $P_{II}$, namely the so called {\it alternate discrete} $P_{II}$, and this connection leads to an expression in terms of the Umemura polynomials for the third Painlev\'{e} equation ($P_{III}$). It is shown that B\"{a}cklund transformation for the alternate discrete Painlev\'{e} equation is a symplectic map, and the shift in time is also symplectic. Finally we present a Lax pair for the alternate discrete $P_{II}$, which recovers Jimbo and Miwa's Lax pair for $P_{II}$ in the continuum limit $h\to 0$.Comment: 23 pages, IOP style. Title changed, and connection with Umemura polynomials adde

Magneto-gyrotropic effects in semiconductor quantum wells (review)

Magneto-gyrotropic photogalvanic effects in quantum wells are reviewed. We discuss experimental data, results of phenomenological analysis and microscopic models of these effects. The current flow is driven by spin-dependent scattering in low-dimensional structures gyrotropic media resulted in asymmetry of photoexcitation and relaxation processes. Several applications of the effects are also considered.Comment: 28 pages, 13 figure

The Hamiltonian Structure of the Second Painleve Hierarchy

In this paper we study the Hamiltonian structure of the second Painleve hierarchy, an infinite sequence of nonlinear ordinary differential equations containing PII as its simplest equation. The n-th element of the hierarchy is a non linear ODE of order 2n in the independent variable $z$ depending on n parameters denoted by ${t}_1,...,{t}_{n-1}$ and $\alpha_n$. We introduce new canonical coordinates and obtain Hamiltonians for the $z$ and $t_1,...,t_{n-1}$ evolutions. We give explicit formulae for these Hamiltonians showing that they are polynomials in our canonical coordinates

Spectral line shape identification with continuous wavelet transform

A lot of methods that allow analyzing of complex contours are known. In the case of the analytical type of the peak is known the least squares method is usually used. Nevertheless, if the noise level is high enough, LSM method can't be used because of the large distortions of the results. In this paper alternative way based on a wavelet-derivative spectroscopy to analyze complex contours is suggested. The efficiency of the method is demonstrated using the model data and experimental IR spectrum of polyetherimide