Magnetoresistance due to edge spin accumulation

Because of spin-orbit interaction, an electrical current is accompanied by a spin current resulting in spin accumulation near the sample edges. Due again to spin-orbit interaction this causes a small decrease of the sample resistance. An applied magnetic field will destroy the edge spin polarization leading to a positive magnetoresistance. This effect provides means to study spin accumulation by electrical measurements. The origin and the general properties of the phenomenological equations describing coupling between charge and spin currents are also discussed.Comment: 4 pages, 3 figures. Minor corrections corresponding to the published versio

Dyakonov-Perel spin relaxation near metal-insulator transition and in hopping transport

In a heavily doped semiconductor with weak spin-orbital interaction the Dyakonov-Perel spin relaxation rate is known to be proportional to the Drude conductivity. We argue that in the case of weak spin-orbital interaction this proportionality goes beyond the Drude mechanism: it stays valid through the metal-insulator transition and in the range of the exponentially small hopping conductivity.Comment: 3 page

"Phase Diagram" of the Spin Hall Effect

We obtain analytic formulas for the frequency-dependent spin-Hall conductivity of a two-dimensional electron gas (2DEG) in the presence of impurities, linear spin-orbit Rashba interaction, and external magnetic field perpendicular to the 2DEG. We show how different mechanisms (skew-scattering, side-jump, and spin precession) can be brought in or out of focus by changing controllable parameters such as frequency, magnetic field, and temperature. We find, in particular, that the d.c. spin Hall conductivity vanishes in the absence of a magnetic field, while a magnetic field restores the skew-scattering and side-jump contributions proportionally to the ratio of magnetic and Rashba fields.Comment: Some typos correcte

Is Fault-Tolerant Quantum Computation Really Possible?

The so-called "threshold" theorem says that, once the error rate per qubit per gate is below a certain value, indefinitely long quantum computation becomes feasible, even if all of the qubits involved are subject to relaxation processes, and all the manipulations with qubits are not exact. The purpose of this article, intended for physicists, is to outline the ideas of quantum error correction and to take a look at the proposed technical instruction for fault-tolerant quantum computation. It seems that the mathematics behind the threshold theorem is somewhat detached from the physical reality, and that some ideal elements are always present in the construction. This raises serious doubts about the possibility of large scale quantum computations, even as a matter of principle.Comment: Based on a talk given at the Future Trends in Microelectronics workshop, Crete, June 2006. 8 pages, 1 figur

Spin Hall effect in a system of Dirac fermions in the honeycomb lattice with intrinsic and Rashba spin-orbit interaction

We consider spin Hall effect in a system of massless Dirac fermions in a graphene lattice. Two types of spin-orbit interaction, pertinent to the graphene lattice, are taken into account - the intrinsic and Rashba terms. Assuming perfect crystal lattice, we calculate the topological contribution to spin Hall conductivity. When both interactions are present, their interplay is shown to lead to some peculiarities in the dependence of spin Hall conductivity on the Fermi level.Comment: 7 pages, 5 figure