Giant Magneto-Oscillations of Electric-Field-Induced Spin Polarization in 2DEG

We consider a disordered two-dimensional electron gas with spin-orbit coupling placed in a perpendicular magnetic field and calculate the magnitude and direction of the electric-field-induced spin polarization. We find that in strong magnetic fields the polarization becomes an oscillatory function of the magnetic field and that the amplitude of these oscillations is parametrically larger than the polarization at zero magnetic field. We show that the enhanced amplitude of the polarization is a consequence of strong electron-hole asymmetry in a quantizing magnetic field.Comment: 6 pages, 3 figure

New Origin For Spin Current And Current-Induced Spin Precession In Magnetic Multilayers

In metallic ferromagnets, an electric current is accompanied by a flux of angula r momentum, also called spin current. In multilayers, spatial variations of the spin current correspond to drive torques exerted on a magnetic layer. These torq ues result in spin precession above a certain current threshold. The usual kind of spin current is associated with translation of the spin-up and spin-down Ferm i surfaces in momentum space. We discuss a different kind of spin current, assoc iated with expansion and contraction of the Fermi surfaces. It is more nonlocal in nature, and may exist even in locations where the electrical current density is zero. It is larger than the usual spin current, in a ratio of 10 or 100, and is dominant in most cases. The new spin current is proportional to the differenc e Delta-mu = 0.001 eV between spin-up and spin-down Fermi levels, averaged over the entire Fermi surface. Conduction processes, spin relaxation, and spin-wave emission in the multilayer can be described by an equivalent electrical circuit resembling an unbalanced dc Wheatstone bridge. And Delta-mu corresponds to the output voltage of the bridge.Comment: 5 pages, 3 figures. To appear in J. Appl. Phys., vol. 89, May 15, 200

Geometrical effects on spin injection: 3D spin drift diffusion model

We discuss a three-dimensional (3D) spin drift diffusion (SDD) model to inject spin from a ferromagnet (FM) to a normal metal (N) or semiconductor (SC). Using this model we investigate the problem of spin injection into isotropic materials like GaAs and study the effect of FM contact area and SC thickness on spin injection. We find that in order to achieve detectable spin injection a small contact area or thick SC samples are essential for direct contact spin injection devices. We investigate the use of thin metal films (Cu) proposed by S.B. Kumar et al. and show that they are an excellent substitute for tunnelling barriers (TB) in the regime of small contact area. Since most tunnelling barriers are prone to pinhole defects, we study the effect of pinholes in AlO tunnelling barriers and show that the reduction in the spin-injection ratio ($\gamma$) is solely due to the effective area of the pinholes and there is no correlation between the number of pinholes and the spin injection ratio.Comment: 5 pages, 6 figures. Accepted by JA

Complete spin polarization of electrons in semiconductor layers and quantum dots

We demonstrate that non-equilibrium electrons in thin nonmagnetic semiconductor layers or quantum dots can be fully spin polarized by means of simultaneous electrical spin injection and extraction. The complete spin polarization is achieved if the thin layers or quantum dots are placed between two ferromagnetic metal contacts with moderate spin injection coefficients and antiparallel magnetizations. The sign of the spin polarization is determined by the direction of the current. Aplications of this effect in spintronics and quantum information processing are discussed

High-frequency spin valve effect in ferromagnet-semiconductor-ferromagnet structure based on precession of injected spins

New mechanism of magnetoresistance, based on tunneling-emission of spin polarized electrons from ferromagnets (FM) into semiconductors (S) and precession of electron spin in the semiconductor layer under external magnetic field, is described. The FM-S-FM structure is considered, which includes very thin heavily doped (delta-doped) layers at FM-S interfaces. At certain parameters the structure is highly sensitive at room-temperature to variations of the field with frequencies up to 100 GHz. The current oscillates with the field, and its relative amplitude is determined only by the spin polarizations of FM-S junctions at relatively large bias voltage.Comment: 5 pages, 2 figures, (v2) new plot with a dependence of current J on magnetic field H added in Fig.2 (top panel), minor amendments in the text; (v3) minor typos corrected. To appear in Phys. Rev. Letter

AC Josephson Effect Induced by Spin Injection

Pure spin currents can be injected and detected in conductors via ferromagnetic contacts. We consider the case when the conductors become superconducting. A DC pure spin current flowing in one superconducting wire towards another superconductor via a ferromagnet contact induces AC voltage oscillations caused by Josephson tunneling of condensate electrons. Quasiparticles simultaneously counterflow resulting in zero total electric current through the contact. The Josephson oscillations can be accompanied by Carlson-Goldman collective modes leading to a resonance in the voltage oscillation amplitude.Comment: 5 page

Triplet supercurrent in ferromagnetic Josephson junctions by spin injection

We show that injecting nonequilibrium spins into the superconducting leads strongly enhances the stationary Josephson current through a superconductor-ferromagnet-superconductor junction. The resulting long-range super-current through a ferromagnet is carried by triplet Cooper pairs that are formed in s-wave superconductors by the combined effects of spin injection and exchange interaction. We quantify the exchange interaction in terms of Landau Fermi-liquid factors. The magnitude and direction of the long-range Josephson current can be manipulated by varying the angles of the injected polarizations with respect to the magnetization in the ferromagnet

Spin magnetotransport in two-dimensional hole systems

Spin current of two-dimensional holes occupying the ground-state subband in an asymmetric quantum well and interacting with static disorder potential is calculated in the presence of a weak magnetic field H perpendicular to the well plane. Both spin-orbit coupling and Zeeman coupling are taken into account. It is shown that the applied electric field excites both the transverse (spin-Hall) and diagonal spin currents, the latter changes its sign at a finite H and becomes greater than the spin-Hall current as H increases. The effective spin-Hall conductivity introduced to describe the spin response in Hall bars is considerably enhanced by the magnetic field in the case of weak disorder and demonstrates a non-monotonic dependence on H.Comment: 4 pages, 2 figures, published in Phys. Rev.

The Level Spacing Distribution Near the Anderson Transition

For a disordered system near the Anderson transition we show that the nearest-level-spacing distribution has the asymptotics $P(s)\propto \exp(-A s^{2-\gamma })$ for s\gg \av{s}\equiv 1 which is universal and intermediate between the Gaussian asymptotics in a metal and the Poisson in an insulator. (Here the critical exponent $0<\gamma<1$ and the numerical coefficient $A$ depend only on the dimensionality $d>2$). It is obtained by mapping the energy level distribution to the Gibbs distribution for a classical one-dimensional gas with a pairwise interaction. The interaction, consistent with the universal asymptotics of the two-level correlation function found previously, is proved to be the power-law repulsion with the exponent $-\gamma$.Comment: REVTeX, 8 pages, no figure