Anomalous Rashba spin splitting in two-dimensional hole systems

It has long been assumed that the inversion asymmetry-induced Rashba spin splitting in two-dimensional (2D) systems at zero magnetic field is proportional to the electric field that characterizes the inversion asymmetry of the confining potential. Here we demonstrate, both theoretically and experimentally, that 2D heavy hole systems in accumulation layer-like single heterostructures show the opposite behavior, i.e., a decreasing, but nonzero electric field results in an increasing Rashba coefficient.Comment: 4 pages, 3 figure

Inter-layer Hall effect in double quantum wells subject to in-plane magnetic fields

We report on a theoretical study of the transport properties of two coupled two-dimensional electron systems subject to in-plane magnetic fields. The charge redistribution in double wells induced by the Lorenz force in crossed electric and magnetic fields has been studied. We have found that the redistribution of the charge and the related inter-layer Hall effect originate in the chirality of diamagnetic currents and give a substantial contribution to the conductivity.Comment: 7 RevTex pages, 4 figures, appendix added and misprint in Eq. (11) correcte

Spin dynamics in high-mobility two-dimensional electron systems

Understanding the spin dynamics in semiconductor heterostructures is highly important for future semiconductor spintronic devices. In high-mobility two-dimensional electron systems (2DES), the spin lifetime strongly depends on the initial degree of spin polarization due to the electron-electron interaction. The Hartree-Fock (HF) term of the Coulomb interaction acts like an effective out-of-plane magnetic field and thus reduces the spin-flip rate. By time-resolved Faraday rotation (TRFR) techniques, we demonstrate that the spin lifetime is increased by an order of magnitude as the initial spin polarization degree is raised from the low-polarization limit to several percent. We perform control experiments to decouple the excitation density in the sample from the spin polarization degree and investigate the interplay of the internal HF field and an external perpendicular magnetic field. The lifetime of spins oriented in the plane of a [001]-grown 2DES is strongly anisotropic if the Rashba and Dresselhaus spin-orbit fields are of the same order of magnitude. This anisotropy, which stems from the interference of the Rashba and the Dresselhaus spin-orbit fields, is highly density-dependent: as the electron density is increased, the kubic Dresselhaus term becomes dominant and reduces the anisotropy.Comment: 13 pages, 6 figure

Generalized line criterion for Gauss-Seidel method

We present a module based criterion, i.e. a sufficient condition based on the absolute value of the matrix coefficients, for the convergence of Gauss-Seidel method (GSM) for a square system of linear algebraic equations, the Generalized Line Criterion (GLC). We prove GLC to be the ''most general'' module based criterion and derive, as GLC corollaries, some previously know and also some new criteria for GSM convergence. Although far more general than the previously known results, the proof of GLC is simpler. The results used here are related to recent research in stability of dynamical systems and control of manufacturing systems

A dc voltage step-up transformer based on a bi-layer \nu=1 quantum Hall system

A bilayer electron system in a strong magnetic field at low temperatures, with total Landau level filling factor nu =1, can enter a strongly coupled phase, known as the (111) phase or the quantum Hall pseudospin-ferromagnet. In this phase there is a large quantized Hall drag resistivity between the layers. We consider here structures where regions of (111) phase are separated by regions in which one of the layers is depleted by means of a gate, and various of the regions are connected together by wired contacts. We note that with suitable designs, one can create a DC step-up transformer where the output voltage is larger than the input, and we show how to analyze the current flows and voltages in such devices

Dynamical Kohn Anomaly in Surface Acoustic Wave Response in Quantum Hall Systems Near ν=1/2\nu = 1/2

The dynamical analog of the Kohn Anomaly image of the Fermi Surface is demonstrated for the response functions to the surface acoustic waves in Quantum Hall Systems near $\nu = 1/2$. Kinks appear in the velocity shift $Delta s/s$ and attenuation coefficient $\Gamma$. The effect is considerably enhanced under periodic modulation and should be observable.Comment: 5 pages, 2 figures, the published versio

SUq(2)SU_q(2) Lattice Gauge Theory

We reformulate the Hamiltonian approach to lattice gauge theories such that, at the classical level, the gauge group does not act canonically, but instead as a Poisson-Lie group. At the quantum level, it then gets promoted to a quantum group gauge symmetry. The theory depends on two parameters - the deformation parameter $\lambda$ and the lattice spacing $a$. We show that the system of Kogut and Susskind is recovered when $\lambda \rightarrow 0$, while QCD is recovered in the continuum limit (for any $\lambda$). We thus have the possibility of having a two parameter regularization of QCD.Comment: 26 pages, LATEX fil

The influence of current and future climate-induced risk on the agricultural sector in East and Central Africa: Sensitizing the ASARECA strategic plan to climate change

Rainfed agriculture is and will remain the dominant source of staple food production for the majority of the rural poor in Eastern and Central Africa (ECA). It is clear that larger investments in agriculture by a broad range of stakeholders will be required if this sector is to meet the food security requirements of tomorrow’s Africa. Many factors contribute to the current low levels of investment, but production uncertainty associated with between- and within-season rainfall variability remains a fundamental constraint to many investors who often overestimate the impact of climate induced uncertainty. The climate of Africa is warmer than it was 100 years ago. Model-based predictions of future greenhouse gas-induced climate change for the continent clearly suggest that this warming will continue and, in most scenarios, accelerate. The projections for rainfall are less uniform; large regional differences exist in rainfall variability. However, there is likely to be an increase in annual mean precipitation in East Africa

Aharonov-Bohm oscillations of a particle coupled to dissipative environments

The amplitude of the Bohm-Aharonov oscillations of a particle moving around a ring threaded by a magnetic flux and coupled to different dissipative environments is studied. The decay of the oscillations when increasing the radius of the ring is shown to depend on the spatial features of the coupling. When the environment is modelled by the Caldeira-Leggett bath of oscillators, or the particle is coupled by the Coulomb potential to a dirty electron gas, interference effects are suppressed beyond a finite length, even at zero temperature. A finite renormalization of the Aharonov-Bohm oscillations is found for other models of the environment.Comment: 6 page

Vortex waistlines and long range fluctuations

We examine the manner in which a linear potential results from fluctuations due to vortices linked with the Wilson loop. Our discussion is based on exact relations and inequalities between the Wilson loop and the vortex and electric flux order parameters. We show that, contrary to the customary naive picture, only vortex fluctuations of thickness of the order of the spatial linear size of the loop are capable of producing a strictly linear potential. An effective theory of these long range fluctuations emerges naturally in the form of a strongly coupled Z(N) lattice gauge theory. We also point out that dynamical fermions introduced in this medium undergo chiral symmetry breaking.Comment: 17 pages, LaTex file with 7 eps figures, revised references, minor comments adde