42 research outputs found
Semiclassical theory of spin-polarized shot noise in mesoscopic diffusive conductors
We study fluctuations of spin-polarized currents in a three-terminal
spin-valve system consisting of a diffusive normal metal wire connected by
tunnel junctions to three ferromagnetic terminals. Based on a spin-dependent
Boltzmann-Langevin equation, we develop a semiclassical theory of charge and
spin currents and the correlations of the currents fluctuations. In the three
terminal system, we show that current fluctuations are strongly affected by the
spin-flip scattering in the normal metal and the spin polarizations of the
terminals, which may point in different directions. We analyze the dependence
of the shot noise and the cross-correlations on the spin-flip scattering rate
in the full range of the spin polarizations and for different magnetic
configurations. Our result demonstrate that noise measurements in
multi-terminal devices allow to determine the spin-flip scattering rate by
changing the polarizations of ferromagnetic terminals.Comment: 12 pages, 5 figure
Universality of Shot-Noise in Multiterminal Diffusive Conductors
We prove the universality of shot-noise in multiterminal diffusive conductors
of arbitrary shape and dimension for purely elastic scattering as well as for
hot electrons. Using a Boltzmann-Langevin approach we reduce the calculation of
shot-noise correlators to the solution of a diffusion equation. We show that
shot-noise in multiterminal conductors is a non-local quantity and that
exchange effects can occur without quantum phase coherence even at zero
electron temperature. Concrete numbers for shot-noise are given that can be
tested experimentally.Comment: 4 double-column pages, REVTeX, 1 eps figure embedded with eps
Minimum-Uncertainty Angular Wave Packets and Quantized Mean Values
Uncertainty relations between a bounded coordinate operator and a conjugate
momentum operator frequently appear in quantum mechanics. We prove that
physically reasonable minimum-uncertainty solutions to such relations have
quantized expectation values of the conjugate momentum. This implies, for
example, that the mean angular momentum is quantized for any
minimum-uncertainty state obtained from any uncertainty relation involving the
angular-momentum operator and a conjugate coordinate. Experiments specifically
seeking to create minimum-uncertainty states localized in angular coordinates
therefore must produce packets with integer angular momentum.Comment: accepted for publication in Physical Review
Coherent Population Trapping of an Electron Spin in a Single Negatively Charged Quantum Dot
Coherent population trapping (CPT) refers to the steady-state trapping of
population in a coherent superposition of two ground states which are coupled
by coherent optical fields to an intermediate state in a three-level atomic
system. Recently, CPT has been observed in an ensemble of donor bound spins in
GaAs and in single nitrogen vacancy centers in diamond by using a fluorescence
technique. Here we report the demonstration of CPT of an electron spin in a
single quantum dot (QD) charged with one electron.Comment: to be appeared in Nature Physic