Note on a sigma model connection with instanton dynamics

It is well known that the instanton approach to QCD generates an effective term which looks like a three flavor determinant of quark bilinears. This has the right behavior to explain the unusual mass and mixing of the $\eta(958)$ meson, as is often simply illustrated with the aid of a linear SU(3) sigma model. It is less well known that the instanton analysis generates another term which has the same transformation property but does not have a simple interpretation in terms of this usual linear sigma model. Here we point out that this term has an interpretation in a generalized linear sigma model containing two chiral nonets. The second chiral nonet is taken to correspond to mesons having two quarks and two antiquarks in their makeup. The generalized model seems to be useful for learning about the spectrum of low lying scalar mesons which have been emerging in the last few years. The physics of the new term is shown to be related to the properties of an "excited" $\eta'$ state present in the generalized model and for which there are some experimental candidates.Comment: reference added, minor typos 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

Spin dynamics in (110)-oriented quantum wells

Quantum structures of III–V semiconductors grown on (1 1 0)-oriented substrates are promising for spintronic applications because they allow us to engineer and control spin dynamics of electrons. We summarise the theoretical ideas, which are the basis for this claim and review experiments to investigate them.<br/

Gated spin relaxation in (1 1 0)-oriented quantum wells

Growth, photoluminescence characterisation and time-resolved optical measurements of electron spin dynamics in (1 1 0)-oriented GaAs/AlGaAs quantum wells are described. Conditions are given for MBE growth of good-quality quantum wells, judged by the width of low-temperature excitonic photoluminescence. At 170 K the electron spin relaxation rate in (1 1 0)-oriented wells shows a 100-fold reduction compared to equivalent (1 0 0)-oriented wells and also a 10-fold increase with applied electric field from 20 to 80 kV cm?1. There is evidence for similar dramatic effects at 300 K. Spin relaxation is field independent below 20 kV cm?1 reflecting quantum well asymmetry. The results indicate the achievability of voltage-gateable quantum well spin memory time longer than 10 ns at room temperature simultaneously with high electron mobility

All optical measurement of Rashba coefficient in quantum wells

We perform an all-optical spin-dynamic measurement of the Rashba spin-orbit interaction in (110)-oriented GaAs/AlGaAs quantum wells under applied electric field. This crystallographic orientation allows us to isolate the Rashba from other contributions, giving precise values of the Rashba coefficient. At low temperature, we find good agreement between our measurements and the k·p theory. Unexpectedly, we observe a temperature dependence of the Rashba coefficient that may signify the importance of higher-order terms of the Rashba coupling