Non-Magnetic Spinguides and Spin Transport in Semiconductors

We propose the idea of a "spinguide", i.e. the semiconductor channel which is surrounded with walls from the diluted magnetic semiconductor (DMS) with the giant Zeeman splitting which are transparent for electrons with the one spin polarization only. These spinguides may serve as sources of a spin-polarized current in non-magnetic conductors, ultrafast switches of a spin polarization of an electric current and, long distances transmission facilities of a spin polarization (transmission distances can exceed a spin-flip length). The selective transparence of walls leads to new size effects in transport.Comment: 4 pages, 2 figure

Angle-Resolved Spectroscopy of Electron-Electron Scattering in a 2D System

Electron-beam propagation experiments have been used to determine the energy and angle dependence of electron-electron (ee) scattering a two-dimensional electron gas (2DEG) in a very direct manner by a new spectroscopy method. The experimental results are in good agreement with recent theories and provide direct evidence for the differences between ee-scattering in a 2DEG as compared with 3D systems. Most conspicuous is the increased importance of small-angle scattering in a 2D system, resulting in a reduced (but energy-dependent) broadening of the electron beam.Comment: 4 pages, 4 figure

The electrical resistance of spatially varied magnetic interface. The role of normal scattering

We investigate the diffusive electron transport in conductors with spatially inhomogeneous magnetic properties taking into account both impurity and normal scattering. It is found that the additional interface resistance that arises due to the magnetic inhomogeneity depends essentially on their spatial characteristics. The resistance is proportional to the spin flip time in the case when the magnetic properties of the conducting system vary smoothly enough along the sample. It can be used to direct experimental investigation of spin flip processes. In the opposite case, when magnetic characteristics are varied sharply, the additional resistance depends essentially on the difference of magnetic properties of the sides far from the interface region. The resistance increases as the frequency of the electron-electron scattering increases. We consider also two types of smooth interfaces: (i) between fully spin-polarized magnetics and usual magnetic (or non-magnetic) conductors, and (ii) between two fully oppositely polarized magnetic conductors. It is shown that the interface resistance is very sensitive to appearing of the fully spin-polarized state under the applied external field

Loop cosmology: regularization vs. quantization

It is argued that it is the regularization of the classical Hamiltonian —the first step in loop cosmology in order to build a well-defined quantum theory— that is already able to avoid the Big Bang and Big Rip singularities, rather than the usually invoked quantum corrections coming from the quantization of the Hamiltonian. To prove such statement, the classical regularized Hamiltonian corresponding to loop gravity is obtained, and it is shown that it coincides, up to terms of order planck, with the so-called effective Hamiltonian which is calculated from the quantum regularized Hamiltonian using semi-classical techniques. From that comparison it is concluded that both types of singularities are avoided at the "classical level" already, i.e., using loop cosmology, in the sense that only the quantum nature of the geometry is invoked (the loop cut-off) in order to construct the regularized Hamiltonian and to fix the parameter on which it depends. Such finding constitutes a key manifestation of the intrinsic power of loop gravity, as compared with other alternatives

On the relationship between microstructure and residual stress in laser-shock-peened Ti-6Al-4V

The relationship between residual stress and microstructure evolution during laser shock peening (LSP) of Ti-6Al-4V was investigated. To this end, the program material was processed using a 5-J Q-switched Nd:YAG laser with a wavelength of 1064 nm and a pulse duration of 20 n