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We studied spin manipulation of 1.85 GeV/c polarized deuteron beam stored in COSY obtaining a spin-flip efficiency of 97±1%. We first discovered experimentally and then explained theoretically interesting behavior of the deuteron tensor polarization. We, for the first time, studied systematically spin resonance strengths induced by rf dipoles and solenoids. We found huge disagreements between the strengths measured in controlled Froissart-Stora sweeps and the theoretical values calculated using the well-known formulae. These data instigated re-examination of these formulae. We tested Chao’s proposed new matrix formalism for describing the spin dynamics due to a single spin resonance, which may be the first fundamental improvement of the Froissart-Stora equation in that it allows analytic calculation of the beam polarization’s behavior inside a resonance. Our measurements of the deuteron’s polarization near and inside the resonance agreed precisely with the Chao formalism’s predicted oscillations. We tested Kondratenko’s proposal to overcome depolarizing resonances by ramping through them with a crossing pattern, which should force the depolarizing contributions to cancel themselves. Our first test of this idea with 2.1 GeV/c protons was not conclusive but a later test with 1.85 GeV/c deuterons demonstrated a rather substantial reduction in the depolarization compared to the tune jump at the same rate. [ABSTRACT FROM AUTHOR]

A unique design feature of a polarized Electron-Ion Collider (ELIC) based on CEBAF is its Figure-8 shaped storage rings for both electrons and ions, which significantly simplifies beam polarization maintenance and manipulation. The CEBAF accelerator is used as a full energy injector of polarized electron beams into the electron storage ring. While electron polarization is maintained vertical in arcs of the ring, a stable longitudinal spin at four collision points is achieved through vertical crossing bending magnets, solenoid spin rotators, and horizontal orbit bends. Spin matching technique needs to be implemented in order to enhance quantum self-polarization and minimize depolarization effects. In this paper, we also discuss several important issues related to the use of positron beams, radiative polarization and quantum depolarization effects, as well as spin in ELIC. [ABSTRACT FROM AUTHOR]

The Chao matrix formalism allows analytic calculations of a beam’s polarization behavior inside a spin resonance. We recently tested its prediction of polarization oscillations occurring in a stored beam of polarized particles near a spin resonance. Using a 1.85 GeV/c polarized deuteron beam stored in COSY, we swept a new rf solenoid’s frequency rather rapidly through 400 Hz during 100 ms, while varying the distance between the sweep’s end frequency and the central frequency of an rf-induced spin resonance. Our measurements of the deuteron’s polarization for sweeps ending near and inside the resonance agree with the Chao formalism’s predicted oscillations. [ABSTRACT FROM AUTHOR]

Pulse sequences with multiple lengths of echo spacings are used in oilfield NMR logging for diffusion-based NMR applications such as rock and fluid characterization. One specific implementation is the so-called diffusion editing sequence comprising two long echo spacings followed by a standard CPMG at a shorter echo spacing. The echoes in the CPMG portion contain signal from both the direct and stimulated echoes. Modern oilfield NMR logging tools are designed for continuous depth logging of earth formations by projecting both the static (B0) and dynamic (B1) fields into the formation. Both B0 and B1 profiles are grossly inhomogeneous which results in non-steady-state behavior in the early echoes. The spin dynamics effects present a challenge for processing the echo amplitudes to measure porosity (amplitude extrapolated to zero time) and attenuations for fluid or pore size characterization. In this work we describe a calculation of the spin dynamics of the diffusion editing sequence with two long echo spacings. The calculation takes into account full B1 and B0 field maps, and comparisons will be made for sensors and parameters typical of oilfield logging tools and environments. [ABSTRACT FROM AUTHOR]

It is widely accepted that quantum wells with potential profiles lacking inversion symmetry will exhibit spin-split conduction band states due to the Rashba spin-orbit interaction. Here we measure conduction band splitting for undoped asymmetric and symmetric GaAs/AlGaAs quantum wells in the absence of electric fields. Surprisingly the conduction band spin-splitting measured in asymmetric quantum wells is no greater than that measured in symmetric quantum wells. This is a consequence of Ehrenfests theorem and the fact that the conduction and valence band edge profiles are related by a constant factor. [ABSTRACT FROM AUTHOR]

The spin dynamics of a single Mn ion confined in a CdTe/(Cd, Mg, Zn)Te quantum dot is determined by measurements of photon correlation of photoluminescence. The characteristic time of spin flip is a few nanoseconds and strongly depends on the excitation power. [ABSTRACT FROM AUTHOR]

Measurements of spin dynamics of electrons in high-mobility, two dimensional electron gases (2DEGs) in GaAs/AlGaAs quantum wells from 5K to 300K show a rapid increase of spin relaxation time up to a peak near the Fermi temperature. Theoretical analysis based on the D’yakonov-Perel’ mechanism shows that this variation is ‘motional slowing’ caused by electron-electron scattering and that the mobility of the electrons plays a minor role in the spin dynamics. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Time-resolved magneto-photoluminescence spectroscopy is applied to elucidate dynamics of excitons in GaAs/AlGaAs/ZnSe/ZnCdMnSe heterovalent double quantum wells (QW). An essential slowdown of the recombination rate was observed, resulting from exciton localization due to the compositional disordering at the AlGaAs/ZnSe heterovalent interface. It was found that both exciton lifetime and spin lifetime can be controlled by varying the detuning of the single-QW electron levels. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We report on both experimental and theoretical study of conduction-electron spin polarization dynamics achieved by pulsed optical pumping at room temperature in GaAs1-xNx alloys with a small nitrogen content (x = 2.1, 2.7, 3.5%). It is found that the photoluminescence (PL) circular polarization reaches 40–45% and this giant value persists within 2 ns. The results are explained by spin-dependent capture of free conduction electrons on deep paramagnetic centers. We have developed a nonlinear theory of spin dynamics in the coupled system of spin-polarized free and localized carriers that describes the experimental dependencies, in particular, electron spin quantum beats observed in a transverse magnetic field. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We report on electron spin quantum beats observed in transverse magnetic field of positively charged excitons in an ensemble of InAs/GaAs quantum dots. We show that two contributions must be taken into account to explain the damping of the circular polarization oscillations: the first one is due to the nuclear field fluctuations experienced by the electron spin from dot to dot. The second one is due to the dispersion on the transverse Landé g-factor, due to the inherent inhomogeneity of the system, and leads to a field dependent contribution to the damping. We have developed a model taking into account both contributions, which is in good agreement with the experimental data. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Generation mechanisms of long-lived spin coherence of two-dimensional electron gas (2DEG) have been studied theoretically and experimentally, the latter by means of a picosecond pump-probe Kerr rotation technique. CdTe/(Cd,Mg)Te quantum wells with a diluted two-dimensional electron gas have been addressed. Strong Coulomb interaction between electrons and holes, which results in large binding energies of neutral and negatively charged excitons (trions), allows selective addressing of exciton and trion states with resonant optical excitation. Different scenarios of coherence generation have been analyzed, namely, direct trion photocreation, formation of trions from photogenerated excitons and electron-exciton exchange scattering. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Time-resolved Kerr rotation (TRKR) Spectroscopy has been applied to a two-dimensional (2D) electron gas in GaAs/AlGaAs hetero-junction to probe the electron and nuclear spin dynamics in quantum Hall regime. A large and long-lasting Kerr rotation signal was ascribed to the high-mobility 2D-electron gas, since the Kerr signal from etched high purity GaAs substrate was much smaller and shorter. In a configuration where an out-of-plane magnetic field quantizes 2D-electrons into Landau levels, the spin coherence time, T2* exhibits a drastic increase. Furthermore, both T2* and effective g factor exhibit an oscillation behavior as a function of the magnetic field. Under a circularly polarized pump, we observed an Overhauser shift up to 40 μeV, which corresponds to 30 % dynamic nuclear polarization (DNP). © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Dynamical properties of the electron and hole spins are demonstrated in double quantum wells composed of diluted magnetic and nonmagnetic semiconductors. Excitonic photoluminescence of the type-II transition appears for the lower-lying down-spin level of the exciton in magnetic field. A type-I exciton transition is also observed for the opposite up-spin exciton state. The result shows the spatial spin separation and the spin-injection dynamics for the heavy-hole spin states in the double quantum wells. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have carried out 1H nuclear magnetic resonance in a one-dimensional ferrimagnet Mn(hfac)2NITiPr formed by Mn2+ (s = 5/2) ions and nitonyl nitroxide radicals (s = 1/2) to investigate the spin dynamics in the system. From the temperature dependence of the NMR spectrum it is revealed that, with decreasing temperature, spin correlations between the Mn2+ and radical spins develop, and that the direction of each spin moment becomes frozen on the time scale of the NMR frequency below 15 K. The dependence of the nuclear relaxation rate (1/T1) on both temperature and magnetic field is also reported. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

High field ESR measurements of powder and aligned samples of MCuP2O7 (M = Sr, Pb) have been performed in the temperature range from 1.7 K to 265 K in the frequency range from 40 GHz to 370 GHz. A typical powder absorption line of Cu2+ is observed in the case of the powder sample. We have found that the g values increase with decreasing temperature below 10 K and these g-shift directions are not consistent with the ESR theory of Nagata-Tazuke for the one dimensional antiferromagnet. A frequency dependence of the g-shift is also observed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Measurements of magnetization and muon spin relaxation (μSR) have been carried out for the sample of Ca3 (Co1-xZnx)2O6 with a frustrated antiferromagnetic triangular lattice consisting of Ising ferromagnetic chains for the purpose of the investigation of Zn-substitution effect on the frustrated system. The magnetic ordering temperature Tc1 determined from magnetization data is 22 K for x = 0.03, which is 3 K lower than that of the un-doped sample. This implies the reduction of an inter-chain interaction due to Zn-substitution, In the μSR measurement in longitudinal fields, static magnetic order could not be observed even at 18 K below Tc1. By Zn-substitution up to 3% in Ca3Co2O6, the magnetic frustration is not removed but rather enhanced due to the reduction of the exchange interaction in nearest and next nearest neighbors. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Highly spin polarized or half-metallic systems are of considerable current interest because of their potential for spin injection in spintronics applications. The ferromagnet (FM) CoS2 is close to being a half-metal. Recent theoretical and experimental work has shown that the alloys Co1-xFexS2 (0.07 < x < 0.9) are highly spin polarized at low temperatures. The Fe concentration may be used to tune the spin polarization. Using 59Co FM- NMR we have investigated the spin dynamics in this family of alloys and have obtained information on the evolution of the d-band density of states at the Fermi level with x in the range 0 to 0.3. The results are compared with available theoretical predictions. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]