Kinetics Of Spin Relaxation Research Articles

Super-long life time for 2D cyclotron spin-flip excitons.

An experimental technique for the indirect manipulation and detection of electron spins entangled in two-dimensional magnetoexcitons has been developed. The kinetics of the spin relaxation has been investigated. Photoexcited spin-magnetoexcitons were found to exhibit extremely slow relaxation in specific quantum Hall systems, fabricated in high mobility GaAs/AlGaAs structures; namely, the relaxation time reaches values over one hundred microseconds. A qualitative explanation of this spin-relaxation kinetics is presented. Its temperature and magnetic field dependencies are discussed within the available theoretical framework.

Effects of magnetic nanoparticles on nuclear spin relaxation in viscous systems

Acceleration of the longitudinal spin relaxation kinetics, associated with the presence of magnetic nanoparticles (MNPs), has been analysed based on the diffusion mechanism of the spin relaxation. The predictions of the outer sphere model were tested in viscous systems and complex multiphase systems, where different components had different mobilities. Depending on the effective size of nanoparticles and molecular mobility, increase, decrease or no changes in the relaxation rate have been observed. The results confirm the applicability of the model to systems with MNPs of ultra-fine size.

Kinetics of spin relaxation in quantum wires and channels: Boundary spin echo and formation of a persistent spin helix

In this paper we use a spin kinetic equation to study spin polarization dynamics in 1D wires and 2D channels. This approach is valid in both diffusive and ballistic spin transport regimes and, therefore, more general than the usual spin drift-diffusion equations. In particular, we demonstrate that in infinite 1D wires with Rashba spin-orbit interaction the exponential spin relaxation decay can be modulated by an oscillating function. In the case of spin relaxation in finite length 1D wires, it is shown that an initially homogeneous spin polarization spontaneously transforms into a persistent spin helix. An interesting sound waves echo-like behavior of initially localized spin polarization packet is found in finite length wires. We show that a propagating spin polarization profile reflects from a system boundary and returns back to its initial position similarly to the reflectance of sound waves from an obstacle. Green's function of spin kinetic equation is found for both finite and infinite 1D systems. Moreover, we demonstrate explicitly that the spin relaxation in 2D channels with Rashba and Dresselhaus spin-orbit interactions of equal strength occurs similarly to that in 1D wires of finite length. Finally, a simple transformation mapping 1D spin kinetic equation into the Klein-Gordon equation with an imaginary mass is found thus establishing an interesting connection between semiconductor spintronics and relativistic quantum mechanics.

EPR spectroscopic characterization of neuronal NO synthase.

Neuronal NO synthase (nNOS) consists of a reductase domain that binds FAD, FMN, NADPH, and calmodulin, and an oxygenase domain that binds heme, tetrahydrobiopterin, and the substrate L-arginine. One flavin in resting nNOS exits as an air-stable semiquinone radical. During NO synthesis, electron transfer occurs between the flavins and heme iron. We have characterized the nNOS heme iron and flavin semiquinone radical by electron paramagnetic resonance (EPR) spectroscopy. Under anaerobic conditions, the flavin radical spin relaxation was very slow (8 HZ at 22 K) and was enhanced 13-fold by dissolved dioxygen via spin-spin coupling. The flavin radical, probably the semiquinone FMNH., was shown by progressive microwave power saturation and EPR saturation recovery under anaerobic conditions to be spin-spin coupled with the heme iron located in the nNOS oxygenase domain. Analysis of an nNOS preparation that was devoid of heme but contained the flavin radical revealed that spin-spin coupling increased the rate of flavin radical relaxation by a factor of 15. The presence of bound substrate (L-arginine) or the substate analogue Nomega-nitro-L-arginine methyl ester (NAME) had no effect on the flavin spin relaxation kinetics. The observed g values of the nNOS heme were 7.68, and 1.81 and were unchanged by occupation of the substrate binding site by L-arginine or NAME. The substrate also had no effect on the heme zero-field splitting parameter, D=5.2cm-1. Together, the data indicate that the flavin and heme redox centers are positioned near each other in nNOS, consistent with their participating in an interdomain electron transfer. The flavin radical is affected by dissolved oxygen, suggesting that its binding site within the reductase domain partially exposed to solvent, but is unaffected when substrate binds to the oxygenase domain. Substrate binding also appears to take place outside the first coordination shell of the nNOS heme iron.

High-density photogenerated free-carrier spin relaxation processes in Wurtzite semiconductors: CdSe and semimagnetic semiconductor Cd/sub 1-x/Mn/sub x/Se

Picosecond time-resolves spin relaxation kinetics of high-density free carriers is investigated at low temperatures on CdSe (x=0) and in the dilute semimagnetic semiconductor Cd/sub 1-x/Mn/sub x/Se for x=0.05 and 0.10. The fast spins relaxation observed in CdSe results from a mechanism associated with the noncentrosymmetric character of the band structure for this material. This process is similar to the one proposed by M.I. D'yakonov and V.I. Perel' (1971) for the zinc blende crystal structures. The spin relaxation times in CdSe are on the order of 30 ps. The spin relaxation time are <20 ps in semimagnetic semiconductor Cd/sub 1-x/MnSe and are consistent with spin-flip Raman scattering measurements. The increase in spin relaxation rate relative to CdSe is explained in terms of the carrier spin exchange between the carriers and the magnetic spin sites. A probable cause for the reduction in the observed spin polarization factor for carriers in Cd/sub 1-x/Mn/sub x/Se (x not=0) is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Population dynamics and spin relaxations of excitons in GaSe

From the transient luminescence behaviour, the formation time and the lifetime of the direct exciton of GaSe are determined to be ≲20 ps and (1÷2) ns, respectively. The grow-up of a stimulated-emission band with time is explained by the light amplification effect. Spin relaxation kinetics of the exciton is studied through optical spin memory of luminescence.