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The weak localization correction to the conductivity of quantum wires with linear Rashba-Dresselhaus spin-orbit coupling is derived analytically as function of wire width W. The spin relaxation rate is found to decrease as W becomes smaller than the spin-precession length L SO . As a result, the sign of the conductivity correction switches to weak localization, positive magnetoconductivity for wire widths smaller than L SO . A relaxation rate due to the cubic Dresselhaus coupling with a corresponding length scale L remains, however, even in narrow wires W L SO . At low temperature, an antilocalization peak with negative magnetoconductivity is therefore recovered when the dephasing length exceeds L . grams to take into account the diffusive motion, yields the quantum correction to the static conductivity [9],

The quantum correction to the conductivity in disordered quantum wires with linear Rashba spin-orbit coupling is obtained. For quantum wires with spin-conserving boundary conditions, we find a crossover from weak antilocalization to weak localization as the wire width W is reduced using exact diagonalization of the Cooperon equation. This crossover is due to the dimensional dependence of the spin relaxation rate of conduction electrons, which becomes diminished, when the wire width W is smaller than the bulk spin precession length L SO . We thus confirm previous results for small wire width, W / L SO Շ 1 ͓S. Kettemann, Phys. Rev. Lett. 98, 176808 ͑2007͔͒, where only the transverse 0 modes of the Cooperon equation had been taken into account. We find that spin helix solutions become stable for arbitrary ratios of linear Rashba and Dresselhaus coupling in narrow wires. For wider wires, the spin relaxation rate is found to be not monotonous as function of wire width W: it becomes first enhanced for W on the order of the bulk spin precession length L SO before it becomes diminished for smaller wire widths. In addition, we find that the spin relaxation is smallest at the edge of the wire for wide wires. The effect of the Zeeman coupling to the magnetic field perpendicular to the 2D electron system ͑2DES͒ is studied and found to result in a modification of the magnetoconductivity: it shifts the crossover from weak antilocalization to weak localization to larger wire widths W c . When the transverse confinement potential of the quantum wire is smooth, the boundary conditions become rather adiabatic. Then, the spin relaxation rate is found to be enhanced as the wire width W is reduced. We find that only a spinpolarized state retains a finite spin relaxation rate in such narrow wires. Thus, we conclude that the injection of polarized spins into nonmagnetic quantum wires should be favorable in wires with smooth confinement potential. Finally, in wires with tubular shape, corresponding to transverse periodic boundary conditions, we find no reduction of the spin relaxation rate.

Low temperature properties of glasses are derived within a generalized tunneling model, considering the motion of charged particles on a closed path in a double-well potential. The presence of a magnetic induction field B violates the time reversal invariance due to the Aharonov-Bohm phase, and leads to flux periodic energy levels. At low temperature, this effect is shown to be strongly enhanced by dipole-dipole and elastic interactions between tunneling systems and becomes measurable. Thus, the recently observed strong sensitivity of the electric permittivity to weak magnetic fields can be explained. In addition, superimposed oscillations as a function of the magnetic field are predicted.Comment: 4 page

Extensive studies of spin transfer and spin relaxation at a ferromagneticnonmagnetic interface 21,22,23 have shown that such a system can act as an effective source

In order to study how local disturbances affect the ac grid stability, we start from nonlinear power balance equations and map them to complex linear wave equations. Having obtained stationary solutions with phases φ_{i} at generator and consumer nodes i, we next study the dynamics of deviations. Starting with an initially localized perturbation, it is found to spread in a periodic grid diffusively throughout the grid. We find the parametric dependence of diffusion constant D. We apply the same solution strategy to general grid topologies and analyze their stability against local perturbations. The perturbation remains either localized or becomes delocalized, depending on grid topology, power capacity, and distribution of consumers and generator power P_{i}. Delocalization is found to increase the lifetime of perturbations and thereby their influence on grid stability, whereas localization results in an exponentially fast decay of perturbations at all grid sites. These results may therefore lead to new strategies to control the stability of electricity grids.

We propose a spin-mechanical device to control and detect spin currents by mechanical torque. Our hybrid nano-electro-mechanical device, which contains a nanowire with a ferromagneticnonmagnetic interface, is designed to measure or induce spin polarized currents. Since spin carries angular momentum, a spin flip or spin transfer process involves a change in angular momentum-and hence, a torque-which enables mechanical measurement of spin flips. Conversely, an applied torque can result in spin polarization and spin current.

A spin injection is achieved in a direct-contact cobalt−single-layer graphene nonlocal spin-valve system, overlaid with a top gate. The spin signal is retained even in bipolar configurations of graphene. Hanle spin-precession analysis demonstrates that proportionality between spin and momentum relaxation times, which supports the Elliot-Yafet-type spin relaxation, holds consistently only when the carrier-density dependence of the density of states is taken into account. The corresponding strong spin-orbit coupling (∼10 meV) suggests that covalently bonded adsorbates, rather than charged impurities, govern the spin relaxation in diffusive graphene.