142,768 research outputs found
Electron Spin Relaxation under Drift in GaAs
Based on a Monte Carlo method, we investigate the influence of transport
conditions on the electron spin relaxation in GaAs. The decay of initial
electron spin polarization is calculated as a function of distance under the
presence of moderate drift fields and/or non-zero injection energies. For
relatively low fields (a couple of kV/cm), a substantial amount of spin
polarization is preserved for several microns at 300 K. However, it is also
found that the spin relaxation rate increases rapidly with the drift field,
scaling as the square of the electron wavevector in the direction of the field.
When the electrons are injected with a high energy, a pronounced decrease is
observed in the spin relaxation length due to an initial increase in the spin
precession frequency. Hence, high-field or high-energy transport conditions may
not be desirable for spin-based devices.Comment: 4 pages, 3 figures, one table. Scheduled for publication in the May
26, 2003 issue of Applied Physics Letters (039321APL
Production of the pentaquark in scattering
We study and processes
for both of the positive and negative parities of the . Employing
the effective chiral Lagrangians for the and interactions, we
calculate differential cross sections as well as total cross sections for the
and reactions. The total
cross sections for the positive-parity turn out to be approximately
ten times larger than those for the negative parity in the range of
the CM energy . The results are
rather sensitive to the mechanism of exchanges in the -- channel.Comment: 9 pages and 11 figure
Generalized BFT Formalism of Electroweak Theory in the Unitary Gauge
We systematically embed the SU(2)U(1) Higgs model in the unitary
gauge into a fully gauge-invariant theory by following the generalized BFT
formalism. We also suggest a novel path to get a first-class Lagrangian
directly from the original second-class one using the BFT fields.Comment: 14 pages, Latex, no figure
Quantum network architecture of tight-binding models with substitution sequences
We study a two-spin quantum Turing architecture, in which discrete local
rotations \alpha_m of the Turing head spin alternate with quantum controlled
NOT-operations. Substitution sequences are known to underlie aperiodic
structures. We show that parameter inputs \alpha_m described by such sequences
can lead here to a quantum dynamics, intermediate between the regular and the
chaotic variant. Exponential parameter sensitivity characterizing chaotic
quantum Turing machines turns out to be an adequate criterion for induced
quantum chaos in a quantum network.Comment: Accepted for publication in J. mod. Optics [Proc. Workshop
"Entanglement and Decoherence", Gargnano (Italy), Sept 1999], 3 figure
Correlation Assisted Phonon Softenings and the Mott-Peierls Transition in VO
To explore the driving mechanisms of the metal-insulator transition (MIT) and
the structural transition in VO2, we have investigated phonon dispersions of
rutile VO2 (R-VO2) in the DFT and the DFT+U (U : Coulomb correlation) band
calculations. We have found that the phonon softening instabilities occur in
both cases, but the softened phonon mode only in the DFT+U describes properly
both the MIT and the structural transition from R-VO2 to monoclinic VO2
(M1-VO2). This feature demonstrates that the Coulomb correlation effect plays
an essential role of assisting the Peierls transition in R-VO2. We have also
found from the phonon dispersion of M1-VO2 that M1 structure becomes unstable
under high pressure. We have predicted a new phase of VO2 at high pressure that
has a monoclinic CaCl2-type structure with metallic nature
Resonance-like electrical control of electron spin for microwave measurement
We demonstrate that the spin-polarized electron current can interact with a
microwave electric field in a resonant manner. The spin-orbit interaction gives
rise to an effective magnetic field proportional to the electric current. In
the presence of both dc and ac electric field components, electron spin
resonance occurs if the ac frequency matches with the spin precession frequency
that is controlled by the dc field. In a device consisting of two
spin-polarized contacts connected by a two-dimensional channel, this mechanism
allows electrically tuned detection of the ac signal frequency and amplitude.
For GaAs, such detection is effective in the frequency domain around tens of
gigahertz.Comment: 10 pages, 2 figure
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