Theory of spin injection

Diffusive theory of spin injection is reviewed and a number of new results is presented for the dc and ac regimes. They were derived by means of the "gamma-technique" allowing to simplify the calculations by choosing the spin injection coefficients through different interfaces as the basic variables. The prospects for increasing spin injection by using resistive spin-selective contacts are emphasized and spin non-conserving contacts are introduced. Finding the basic parameters of a junction from the ac data is discussed.Comment: 4 pages, 2 column REVTeX, to be published in Proceedings of Intern. Symposium on Mesoscopic Superconductivity and Spintronics (Atsugi, March 2002

Diffusion theory of spin injection through resistive contacts

Insertion of a resistive contact between a ferromagnetic metal and a semiconductor microstructure is of critical importance for achieving efficient spin injection into a semiconductor. However, the equations of the diffusion theory are rather cumbersome for the junctions including such contacts. A technique based on deriving a system of self-consistent equations for the coefficients of spin injection, "gamma", through different contacts are developed. These equations are concise when written in the proper notations. Moreover, the resistance of a two-contact junction can be expressed in terms of "gamma"'s of both contacts. This equation makes calculating the spin valve effect straightforward, allows to find an explicit expression for the junction resistance and to prove that its nonequilibrium part is positive. Relation of these parameters to different phenomena like spin-e.m.f. and the junction transients is established. Comparative effect of the Coulomb screening on different parameters is clarified. It is also shown that the spin non-conservation in a contact can have a dramatic effect on the non-equilibrium resistance of the junction.Comment: 16 pages, 2 column REVTeX format, minor editorial changes, references to recent papers added, to appear in Euro. Phys. Journal

Complex impedance of a spin injecting junction

Theory of the ac spin injection from a ferromagnetic electrode into a normal conductor through a tunnel or Schottky contact is developed. Diffusion and relaxation of non-equilibrium spins results in a frequency dependent complex impedance controlled by the spin relaxation rates and the resistances involved. Explicit expression for the impedance is presented. Experimental investigation of the frequency dependence of the impedance should allow measuring spin relaxation times in both conductors, their effective resistances, and also the parameters of the contact controlling the spin injection.Comment: 3 pages, 2 column REVTeX, to appear in Appl. Phys. Let

Mechanism of half-frequency electric dipole spin resonance in double quantum dots: Effect of nonlinear charge dynamics inside the singlet manifold

Electron dynamics in quantum dots manifests itself in spin-flip spectra through electric dipole spin resonance (EDSR). Near a neutrality point separating two different singlet charged states of a double quantum dot, charge dynamics inside a $2\times2$ singlet manifold can be described by a 1/2-pseudospin. In this region, charge dynamics is highly nonlinear and strongly influenced by flopping its soft pseudospin mode. As a result, the responses to external driving include first and second harmonics of the driving frequency and their Raman satellites shifted by the pseudospin frequency. In EDSR spectra of a spin-orbit couplet doublet dot, they manifest themselves as charge satellites of spin-flip transitions. The theory describes gross features of the anomalous half-frequency EDSR in spin blockade spectra [Laird et al., Semicond. Sci. Techol. {\bf 24}, 064004 (2009)].Comment: One figure, one equation, comments adde

Quantum nanostructures in strongly spin-orbit coupled two-dimensional systems

Recent progress in experimental studies of low-dimensional systems with strong spin-orbit coupling poses a question on the effect of this coupling on the energy spectrum of electrons in semiconductor nanostructures. It is shown in the paper that this effect is profound in the strong coupling limit. In circular quantum dots a soft mode develops, in strongly elongated dots electron spin becomes protected from the effects of the environment, and the lower branch of the energy spectrum of quantum wires becomes nearly flat in a wide region of the momentum space.Comment: 5 pages, 1 figur