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Search Results: 1 - 10 of 2501 matches for " Oleg Chalaev "
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Matrices, bases and matrix elements for cubic double crystallographic groups
Oleg Chalaev
Physics , 2012,
Abstract: Matrices of the irreducible representations of double crystallographic point groups O, Td, Ox{1,I} and Tdx{1,I} are derived. The characteristic polynomials (spinor bases) up to the sixth power are obtained. The method for the derivation of the general form of an arbitrary matrix element of a vector/tensor quantity is developed; as an application, the kp matrix elements are calculated. It is demonstrated that the other known method for obtaining the bases of the irreducible representations of the double groups (LS-diagonalization of a linear combination of spherical harmonics) is unreliable.
Coulomb-induced Rashba spin-orbit coupling in semiconductor quantum wells
Oleg Chalaev,G. Vignale
Physics , 2010, DOI: 10.1103/PhysRevLett.104.226601
Abstract: In the absence of an external field, the Rashba spin-orbit interaction (SOI) in a two-dimensional electron gas in a semiconductor quantum well arises entirely from the screened electrostatic potential of ionized donors. We adjust the wave functions of a quantum well so that electrons occupying the first (lowest) subband conserve their spin projection along the growth axis (Sz), while the electrons occupying the second subband precess due to Rashba SOI. Such a specially designed quantum well may be used as a spin relaxation trigger: electrons conserve Sz when the applied voltage (or current) is lower than a certain threshold V*; higher voltage switches on the Dyakonov-Perel spin relaxation.
Spin orbit-induced anisotropic conductivity of a disordered 2DEG
Oleg Chalaev,Daniel Loss
Physics , 2009, DOI: 10.1103/PhysRevB.80.035305
Abstract: We present a semi-automated computer-assisted method to generate and calculate diagrams in the disorder averaging approach to disordered 2D conductors with intrinsic spin-orbit interaction (SOI). As an application, we calculate the effect of the SOI on the charge conductivity for disordered 2D systems and rings in the presence of Rashba and Dresselhaus SOI. In an infinite-size 2D system, anisotropic corrections to the conductivity tensor arise due to phase-coherence and the interplay of Rashba and Dresselhaus SOI. The effect is more pronounced in the quasi-onedimensional case, where the conductivity becomes anisotropic already in the presence of only one type of SOI. The anisotropy further increases if the time-reversal symmetry of the Hamiltonian is broken.
Anisotropic conductivity of disordered 2DEGs due to spin-orbit interactions
Oleg Chalaev,Daniel Loss
Physics , 2007, DOI: 10.1103/PhysRevB.77.115352
Abstract: We show that the conductivity tensor of a disordered two-dimensional electron gas becomes anisotropic in the presence of both Rashba and Dresselhaus spin-orbit interactions (SOI). This anisotropy is a mesoscopic effect and vanishes with vanishing charge dephasing time. Using a diagrammatic approach including zero, one, and two-loop diagrams, we show that a consistent calculation needs to go beyond a Boltzmann equation approach. In the absence of charge dephasing and for zero frequency, a finite anisotropy \sigma_{xy} e^2/lhpf arises even for infinitesimal SOI.
Spin-Hall conductivity due to Rashba spin-orbit interaction in disordered systems
Oleg Chalaev,Daniel Loss
Physics , 2004, DOI: 10.1103/PhysRevB.71.245318
Abstract: We consider the spin-Hall current in a disordered two-dimensional electron gas in the presence of Rashba spin-orbit interaction. We derive a generalized Kubo-Greenwood formula for the spin-Hall conductivity $\sigma$ and evaluate it in an systematic way using standard diagrammatic techniques for disordered systems. We find that in the diffusive regime both Boltzmann and the weak localization contributions to $\sigma$ are of the same order and vanish in the zero frequency limit. We show that the uniform spin current is given by the total time derivative of the magnetization from which we can conclude that the spin current vanishes exactly in the stationary limit. This conclusion is valid for arbitrary spin-independent disorder, external electric field strength, and also for interacting electrons.
Donor-driven spin relaxation in multi-valley semiconductors
Yang Song,Oleg Chalaev,Hanan Dery
Physics , 2014, DOI: 10.1103/PhysRevLett.113.167201
Abstract: We present a theory for spin relaxation of electrons due to scattering off the central-cell potential of impurities in silicon. Taking into account the multivalley nature of the conduction band and the violation of translation symmetry, the spin-flip amplitude is dominated by this short-range impurity scattering after which the electron is transferred to a valley on a different axis in $k$-space (the so called $f$-process). These $f$-processes dominate the spin relaxation at all temperatures, where scattering off the impurity central-cell dominate at low temperatures, and scattering with $\Sigma$-axis phonons at elevated temperatures. To the best of our knowledge, the theory is the first to explain and accurately quantify the empirically-found dependence of spin relaxation on the impurity identity. Accordingly, the new formalism fills a longstanding gap in the spin relaxation theory of $n$-type silicon, and it is valuable for characterization of silicon-based spintronic devices.
Spin-orbit interaction from low-symmetry localized defects in semiconductors
Oleg Chalaev,G. Vignale,Michael E. Flatté
Physics , 2011, DOI: 10.1209/0295-5075/98/17013
Abstract: The presence of low-symmetry impurities or defect complexes in the zinc-blende direct-gap semiconductors (e.g. interstitials, DX-centers) results in a novel spin-orbit term in the effective Hamiltonian for the conduction band. The new extrinsic spin-orbit interaction is proportional to the matrix element of the defect potential between the conduction and the valence bands. Because this interaction arises already in the first order of the expansion of the effective Hamiltonian in powers of Uext/Eg << 1 (where Uext is the pseudopotential of an interstitial atom, and Eg is the band gap), its contribution to the spin relaxation rate may exceed that of the previously studied extrinsic contributions, even for moderate concentrations of impurities.
Aharonov-Bohm magnetization of mesoscopic rings caused by inelastic relaxation
O. L. Chalaev,V. E. Kravtsov
Physics , 2002, DOI: 10.1103/PhysRevLett.89.176601
Abstract: The magnetization of a system of many mesoscopic rings under non-equilibrium conditions is considered. The corresponding disorder-averaged current in a ring is shown to be a sum of the `thermodynamic' and `kinetic' contributions both resulting from the electron-electron interaction. The thermodynamic part can be expressed through the diagonal matrix elements of the current operator in the basis of exact many-body eigenstates and is a generalization of the equilibrium persistent current. The novel kinetic part is present only out of equilibrium and is governed by the off-diagonal matrix elements. It has drastically different temperature and magnetic field behavior.
Function Approximation Using Robust Radial Basis Function Networks  [PDF]
Oleg Rudenko, Oleksandr Bezsonov
Journal of Intelligent Learning Systems and Applications (JILSA) , 2011, DOI: 10.4236/jilsa.2011.31003
Abstract: Resistant training in radial basis function (RBF) networks is the topic of this paper. In this paper, one modification of Gauss-Newton training algorithm based on the theory of robust regression for dealing with outliers in the framework of function approximation, system identification and control is proposed. This modification combines the numerical ro- bustness of a particular class of non-quadratic estimators known as M-estimators in Statistics and dead-zone. The al- gorithms is tested on some examples, and the results show that the proposed algorithm not only eliminates the influence of the outliers but has better convergence rate then the standard Gauss-Newton algorithm.
Calculation of Standard Thermodynamic Potentials for Na-Zeolites with the Use of Linear Programming Problems  [PDF]
Oleg Viacheslavovich Yeriomin
International Journal of Geosciences (IJG) , 2011, DOI: 10.4236/ijg.2011.23024
Abstract: Linear programming problems for Na-Al-Si-O-H system have been formulated and solved for calculations of standard enthalpies and Gibbs potentials of zeolites with unknown thermodynamic properties. The calculations are based on dual solutions of linear programming problems. Comparison of numerical results with published data gives relative mistakes of estimations less than one percent. On the basis of calculated potentials the standard entropies have been estimated. The standard thermodynamic potentials for eight natural zeolites with unknown properties have been calculated. The presented method does not demand any information about crystal structure of zeolites and can be applied to any of their stoichiometric presentation.
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