Weak momentum scattering and the conductivity of graphene

Electrical transport in graphene offers a fascinating parallel to spin transport in semiconductors including the spin-Hall effect. In the weak momentum scattering regime the steady-state density matrix contains two contributions, one linear in the carrier number density $n$ and characteristic scattering time $\tau$, the other independent of either. In this paper we take the Liouville equation as our starting point and demonstrate that these two contributions can be identified with pseudospin conservation and non-conservation respectively, and are connected in a non-trivial manner by scattering processes. The scattering term has a distinct form, which is peculiar to graphene and has important consequences in transport. The contribution linear in $\tau$ is analogous to the part of the spin density matrix which yields a steady state spin density, while the contribution independent of $\tau$, is analogous to the part of the spin density matrix which yields a steady state spin current. Unlike in systems with spin-orbit interactions, the $n$ and $\tau$-independent part of the conductivity is reinforced in the weak momentum scattering regime by scattering between the conserved and non-conserved pseudospin distributions.Comment: 10 pages. Accepted for publication in Phys. Rev.

Statistical characterization of phenolic-novolak structures

Three statistical methods of general validity are valuable for characterizing any polymer which results from chain polymerization of multifunctional branching monomers linked through bifunctional monomers

Effect of discontinuities in surface catalytic activity on laminar heat transfer in arc-heated nitrogen streams

Discontinuity effects in surface catalytic activity on laminar heat transfer in arc heated nitrogen stream

Shot Noise of Spin-Decohering Transport in Spin-Orbit Coupled Nanostructures

We generalize the scattering theory of quantum shot noise to include the full spin-density matrix of electrons injected from a spin-filtering or ferromagnetic electrode into a quantum-coherent nanostructure governed by various spin-dependent interactions. This formalism yields the spin-resolved shot noise power for different experimental measurement setups--with ferromagnetic source and ferromagnetic or normal drain electrodes--whose evaluation for the diffusive multichannel quantum wires with the Rashba (SO) spin-orbit coupling shows how spin decoherence and dephasing lead to substantial enhancement of charge current fluctuations (characterized by Fano factors $> 1/3$). However, these processes and the corresponding shot noise increase are suppressed in narrow wires, so that charge transport experiments measuring the Fano factor $F_{\uparrow \to \uparrow \downarrow}$ in a ferromagnet/SO-coupled-wire/paramagnet setup also quantify the degree of phase-coherence of transported spin--we predict a one-to-one correspondence between the magnitude of the spin polarization vector and $F_{\uparrow \to \uparrow \downarrow}$.Comment: 8 pages, 3 figure; enhanced with 2 new figure

Generation of spin currents and spin densities in systems with reduced symmetry

We show that the spin-current response of a semiconductor crystal to an external electric field is considerably more complex than previously assumed. While in systems of high symmetry only the spin-Hall components are allowed, in systems of lower symmetry other non-spin-Hall components may be present. We argue that, when spin-orbit interactions are present only in the band structure, the distinction between intrinsic and extrinsic contributions to the spin current is not useful. We show that the generation of spin currents and that of spin densities in an electric field are closely related, and that our general theory provides a systematic way to distinguish between them in experiment. We discuss also the meaning of vertex corrections in systems with spin-orbit interactions.Comment: 4 page

Static inverters which sum a plurality of waves Patent

Describing static inverter with single or multiple phase outpu

Imaging spin flows in semiconductors subject to electric, magnetic, and strain fields

Using scanning Kerr microscopy, we directly acquire two-dimensional images of spin-polarized electrons flowing laterally in bulk epilayers of n:GaAs. Optical injection provides a local dc source of polarized electrons, whose subsequent drift and/or diffusion is controlled with electric, magnetic, and - in particular - strain fields. Spin precession induced by controlled uniaxial stress along the axes demonstrates the direct k-linear spin-orbit coupling of electron spin to the shear (off-diagonal) components of the strain tensor.Comment: 5 pages, 5 color figure

Spin precession and alternating spin polarization in spin-3/2 hole systems

The spin density matrix for spin-3/2 hole systems can be decomposed into a sequence of multipoles which has important higher-order contributions beyond the ones known for electron systems [R. Winkler, Phys. Rev. B \textbf{70}, 125301 (2004)]. We show here that the hole spin polarization and the higher-order multipoles can precess due to the spin-orbit coupling in the valence band, yet in the absence of external or effective magnetic fields. Hole spin precession is important in the context of spin relaxation and offers the possibility of new device applications. We discuss this precession in the context of recent experiments and suggest a related experimental setup in which hole spin precession gives rise to an alternating spin polarization.Comment: 4 pages, 2 figures, to appear in Physical Review Letter

Determination of Gd concentration profile in UO2-Gd2O3 fuel pellets

A transversal mapping of the Gd concentration was measured in UO2-Gd2O3 nuclear fuel pellets by electron paramagnetic resonance spectroscopy (EPR). The quantification was made from the comparison with a Gd2O3 reference sample. The nominal concentration in the pellets is UO2: 7.5 % Gd2O3. A concentration gradient was found, which indicates that the Gd2O3 amount diminishes towards the edges of the pellets. The concentration varies from (9.3 +/- 0.5)% in the center to (5.8 +/- 0.3)% in one of the edges. The method was found to be particularly suitable for the precise mapping of the distribution of Gd3+ ions in the UO2 matrix.Comment: 10 pages, 5 figures, 2 tables. Submitted to Journal of Nuclear Material

On the nature of steady states of spin distributions in the presence of spin-orbit interactions

In the presence of spin-orbit interactions, the steady state established for spin distributions in an electric field is qualitatively different from the steady state for charge distributions. This is primarily because the steady state established for spin distributions involves spin precession due to spin-orbit coupling. We demonstrate in this work that the spin density matrix in an external electric field acquires two corrections with different dependencies on the characteristic momentum scattering time. One part is associated with conserved spins, diverges in the clean limit and is responsible for the establishment of a steady-state spin density in electric fields. Another part is associated with precessing spins, is finite in the clean limit and is responsible for the establishment of spin currents in electric fields. Scattering between these distributions has important consequences for spin dynamics and spin-related effects in general, and explains some recent puzzling observations, which are captured by our unified theory.Comment: 10 pages, 1 figur