Shot noise in a diffusive F-N-F spin valve

Fluctuations of electric current in a spin valve consisting of a diffusive conductor connected to ferromagnetic leads and operated in the giant magnetoresistance regime are studied. It is shown that a new source of fluctuations due to spin-flip scattering enhances strongly shot noise up to a point where the Fano factor approaches the full Poissonian value.Comment: 5 pages, 3 figure

Whitney-Sullivan constructions for transitive lie algebroids - smooth case

Let M be a smooth manifold, smoothly triangulated by a simplicial complex K, and A a transitive Lie algebroid on M. A piecewise smooth form on A is a family ω=(ωΔ)Δ∈K such that ωΔ is a smooth form on the Lie algebroid restriction of A to Δ, satisfying the compatibility condition concerning the restrictions of ωΔ to the faces of Δ, that is, if Δ′ is a face of Δ, the restriction of the form ωΔ to the simplex Δ′ coincides with the form ωΔ′. The set Ω∗(A;K) of all piecewise smooth forms on A is a cochain algebra. There exists a natural morphism Ω∗(A;M)→Ω∗(A;K) of cochain algebras given by restriction of a smooth form defined on A to a smooth form defined on the Lie algebroid restriction of A to the simplex Δ, for all simplices Δ of K. In this paper, we prove that, for triangulated compact manifolds, the cohomology of this construction is isomorphic to the Lie algebroid cohomology of A, in which that isomorphism is induced by the restriction mapping.(undefined

Diagrammatic Quantum Monte Carlo for Two-Body Problem: Exciton

We present a novel method for precise numerical solution of the irreducible two-body problem and apply it to excitons in solids. The approach is based on the Monte Carlo simulation of the two-body Green function specified by Feynman's diagrammatic expansion. Our method does not rely on the specific form of the electron and hole dispersion laws and is valid for any attractive electron-hole potential. We establish limits of validity of the Wannier (large radius) and Frenkel (small radius) approximations, present accurate data for the intermediate radius excitons, and give evidence for the charge transfer nature of the monopolar exciton in mixed valence materials.Comment: 4 pages, 5 figure

Intersubband Edge Singularity in Metallic Nanotubes

Tunneling density of states of both the massless and massive (gapped) particles in metallic carbon nanotubes is known to have anomalous energy dependence. This is the result of coupling to multiple low-energy bosonic excitation (plasmons). For both kinds of particles the ensuing effect is the suppression of the density of states by electron-electron interactions. We demonstrate that the optical absorption between gapless and gapped states is affected by the many-body effects in the opposite way. The absorption probability is enhanced compared with the non-interacting value and develops a power-law frequency dependence with the exponent -0.2 for typical nanotubes.Comment: 4 pages, 1 figure (final version, discussion of Sommerfeld factor and Ref. 11 added

Raman scattering in a two-dimensional electron gas: Boltzmann equation approach

The inelastic light scattering in a 2-d electron gas is studied theoretically using the Boltzmann equation techniques. Electron-hole excitations produce the Raman spectrum essentially different from the one predicted for the 3-d case. In the clean limit it has the form of a strong non-symmetric resonance due to the square root singularity at the electron-hole frequency $\omega = vk$ while in the opposite dirty limit the usual Lorentzian shape of the cross section is reestablished. The effects of electromagnetic field are considered self-consistently and the contribution from collective plasmon modes is found. It is shown that unlike 3-d metals where plasmon excitations are unobservable (because of very large required transfered frequencies), the two-dimensional electron system gives rise to a low-frequency ($\omega \propto k^{1/2}$) plasmon peak. A measurement of the width of this peak can provide data on the magnitude of the electron scattering rate.Comment: 4 pages, 3 figures. to appear in Phys. Rev. B 59 (1999