Spin Orientation of Holes in Quantum Wells

This paper reviews the spin orientation of spin-3/2 holes in quantum wells. We discuss the Zeeman and Rashba spin splitting in hole systems that are qualitatively different from their counterparts in electron systems. We show how a systematic understanding of the unusual spin-dependent phenomena in hole systems can be gained using a multipole expansion of the spin density matrix. As an example we discuss spin precession in hole systems that can give rise to an alternating spin polarization. Finally, we discuss the qualitatively different regimes of hole spin polarization decay in clean and dirty samples.Comment: 14 pages, 8 figure

Extrinsic Entwined with Intrinsic Spin Hall Effect in Disordered Mesoscopic Bars

We show that pure spin Hall current, flowing out of a four-terminal phase-coherent two-dimensional electron gas (2DEG) within inversion asymmetric semiconductor heterostructure, contains contributions from both the extrinsic mechanisms (spin-orbit dependent scattering off impurities) and the intrinsic ones (due to the Rashba coupling). While the extrinsic contribution vanishes in the weakly and strongly disordered limits, and the intrinsic one dominates in the quasiballistic limit, in the crossover transport regime the spin Hall conductance, exhibiting sample-to-sample large fluctuations and sign change, is not simply reducible to either of the two mechanisms, which can be relevant for interpretation of experiments on dirty 2DEGs [V. Sih et al., Nature Phys. 1, 31 (2005)].Comment: 5 pages, 3 color EPS figure

Laser in the axial electric field as a tool to search for P-, T- invariance violation

We consider rotation of polarization plane of the laser light when a gas laser is placed in a longitudinal electric field (10~kV/cm). It is shown that residual anisotropy of the laser cavity 10^{-6} and the sensitivity to the angle of polarization plane rotation about 10^{-11} -10^{-12} rad allows one to measure an electron EDM with the sensitivity about 10^{-30} e cm.Comment: 12 page

Phonon-induced decay of the electron spin in quantum dots

We study spin relaxation and decoherence in a GaAs quantum dot due to spin-orbit interaction. We derive an effective Hamiltonian which couples the electron spin to phonons or any other fluctuation of the dot potential. We show that the spin decoherence time $T_2$ is as large as the spin relaxation time $T_1$, under realistic conditions. For the Dresselhaus and Rashba spin-orbit couplings, we find that, in leading order, the effective magnetic field can have only fluctuations transverse to the applied magnetic field. As a result, $T_2=2T_1$ for arbitrarily large Zeeman splittings, in contrast to the naively expected case $T_2\ll T_1$. We show that the spin decay is drastically suppressed for certain magnetic field directions and values of the Rashba coupling constant. Finally, for the spin coupling to acoustic phonons, we show that $T_2=2T_1$ for all spin-orbit mechanisms in leading order in the electron-phonon interaction.Comment: 5 pages, 1 figur

Effect of nonequilibrium phonons on hot-electron spin relaxation in n-type GaAs quantum wells

We have studied the effect of nonequilibrium longitudinal optical phonons on hot-electron spin relaxation in $n$-type GaAs quantum wells. The longitudinal optical phonons, due to the finite relaxation rate, are driven to nonequilibrium states by electrons under an in-plane electric field. The nonequilibrium phonons then in turn influence the electron spin relaxation properties via modifying the electron heating and drifting. The spin relaxation time is elongated due to the enhanced electron heating and thus the electron-phonon scattering in the presence of nonequilibrium phonons. The frequency of spin precession, which is roughly proportional to the electron drift velocity, can be either increased (at low electric field and/or high lattice temperature) or decreased (at high electric field and/or low lattice temperature). The nonequilibrium phonon effect is more pronounced when the electron density is high and the impurity density is low.Comment: 6 pages, 3 figure

Anderson Transitions: Criticality, Symmetries, and Topologies

The physics of Anderson transitions between localized and metallic phases in disordered systems is reviewed. We focus on the character of criticality as well as on underlying symmetries and topologies that are crucial for understanding phase diagrams and the critical behavior.Comment: 36 pages. Published in "50 Years of Anderson Localization", ed. by E. Abrahams (World Scientific, 2010); reprinted in IJMP

Spontaneous Branching of Anode-Directed Streamers between Planar Electrodes

Non-ionized media subject to strong fields can become locally ionized by penetration of finger-shaped streamers. We study negative streamers between planar electrodes in a simple deterministic continuum approximation. We observe that for sufficiently large fields, the streamer tip can split. This happens close to Firsov's limit of `ideal conductivity'. Qualitatively the tip splitting is due to a Laplacian instability quite like in viscous fingering. For future quantitative analytical progress, our stability analysis of planar fronts identifies the screening length as a regularization mechanism.Comment: 4 pages, 6 figures, submitted to PRL on Nov. 16, 2001, revised version of March 10, 200

Conduction band spin splitting and negative magnetoresistance in A3B5{\rm A}_3{\rm B}_5 heterostructures

The quantum interference corrections to the conductivity are calculated for an electron gas in asymmetric quantum wells in a magnetic field. The theory takes into account two different types of the spin splitting of the conduction band: the Dresselhaus terms, both linear and cubic in the wave vector, and the Rashba term, linear in wave vector. It is shown that the contributions of these terms into magnetoconductivity are not additive, as it was traditionally assumed. While the contributions of all terms of the conduction band splitting into the D'yakonov--Perel' spin relaxation rate are additive, in the conductivity the two linear terms cancel each other, and, when they are equal, in the absence of the cubic terms the conduction band spin splitting does not show up in the magnetoconductivity at all. The theory agrees very well with experimental results and enables one to determine experimentally parameters of the spin-orbit splitting of the conduction band.Comment: 8 pages, RevTeX, 4 Postscript figure

Spin relaxation in low-dimensional systems

We review some of the newest findings on the spin dynamics of carriers and excitons in GaAs/GaAlAs quantum wells. In intrinsic wells, where the optical properties are dominated by excitonic effects, we show that exciton-exciton interaction produces a breaking of the spin degeneracy in two-dimensional semiconductors. In doped wells, the two spin components of an optically created two-dimensional electron gas are well described by Fermi-Dirac distributions with a common temperature but different chemical potentials. The rate of the spin depolarization of the electron gas is found to be independent of the mean electron kinetic energy but accelerated by thermal spreading of the carriers.Comment: 1 PDF file, 13 eps figures, Proceedings of the 1998 International Workshop on Nanophysics and Electronics (NPE-98)- Lecce (Italy

Dephasing Times in a Non-degenerate Two-Dimensional Electron Gas

Studies of weak localization by scattering from vapor atoms for electrons on a liquid helium surface are reported. There are three contributions to the dephasing time. Dephasing by the motion of vapor atoms perpendicular to the surface is studied by varying the holding field to change the characteristic width of the electron layer at the surface. A change in vapor density alters the quasi-elastic scattering length and the dephasing due to the motion of atoms both perpendicular and parallel to the surface. Dephasing due to the electron-electron interaction is dependent on the electron density.Comment: 4 pages, Revte