230,924 research outputs found
Spin Dynamics in the Second Subband of a Quasi Two Dimensional System Studied in a Single Barrier Heterostructure by Time Resolved Kerr Rotation
By biasing a single barrier heterostructure with a 500nm-thick GaAs layer as
the absorption layer, the spin dynamics for both of the first and second
subband near the AlAs barrier are examined. We find that when simultaneously
scanning the photon energy of both the probe and pump beams, a sign reversal of
the Kerr rotation (KR) takes place as long as the probe photons break away the
first subband and probe the second subband. This novel feature, while stemming
from the exchange interaction, has been used to unambiguously distinguish the
different spin dynamics ( and ) for the first and second
subbands under the different conditions by their KR signs (negative for
and positive for ). In the zero magnetic field, by scanning
the wavelength towards the short wavelength, decreases in accordance
with the D'yakonov-Perel' (DP) spin decoherence mechanism. At 803nm,
(450ps) becomes ten times longer than (50ps). However, the
value of at 803nm is roughly the same as the value of at
815nm. A new feature has been disclosed at the wavelength of 811nm under the
bias of -0.3V (807nm under the bias of -0.6V) that the spin coherence times
( and ) and the effective factors ( and
) all display a sudden change, due to the "resonant" spin exchange
coupling between two spin opposite bands.Comment: 9pages, 3 figure
Generation of a crowned pinion tooth surface by a surface of revolution
A method of generating crowned pinion tooth surfaces using a surface of revolution is developed. The crowned pinion meshes with a regular involute gear and has a prescribed parabolic type of transmission errors when the gears operate in the aligned mode. When the gears are misaligned the transmission error remains parabolic with the maximum level still remaining very small (less than 0.34 arc sec for the numerical examples). Tooth contact analysis (TCA) is used to simulate the conditions of meshing, determine the transmission error, and determine the bearing contact
Coherent Inverse Photoemission Spectrum for Gutzwiller Projected Superconductors
Rigorous relations for Gutzwiller projected BCS states are derived. The
obtained results do not depend on the details of model systems, but solely on
the wave functions. Based on the derived relations, physical consequences are
discussed for strongly correlated superconducting states such as high- cuprate superconductors.Comment: 4 pages, 3 figures, to be published in Phys. Rev.
Evolution of Surface Deformations of Weakly-Bound Nuclei in the Continuum
We study weakly-bound deformed nuclei based on the coordinate-space Skyrme
Hartree-Fock-Bogoliubov approach, in which a large box is employed for treating
the continuum and surface diffuseness. Approaching the limit of core-halo
deformation decoupling, calculations found an exotic "egg"-like structure
consisting of a spherical core plus a prolate halo in Ne, in which the
resonant continuum plays an essential role. Generally the halo probability and
the decoupling effect in heavy nuclei are reduced compared to light nuclei, due
to denser level densities around Fermi surfaces. However, deformed halos in
medium-mass nuclei are possible with sparse levels of negative parity, for
example, in Ge. The surface deformations of pairing density
distributions are also influenced by the decoupling effect and are sensitive to
the effective pairing Hamiltonian.Comment: 5 pages and 5 figure
Multiple scattering in random mechanical systems and diffusion approximation
This paper is concerned with stochastic processes that model multiple (or
iterated) scattering in classical mechanical systems of billiard type, defined
below. From a given (deterministic) system of billiard type, a random process
with transition probabilities operator P is introduced by assuming that some of
the dynamical variables are random with prescribed probability distributions.
Of particular interest are systems with weak scattering, which are associated
to parametric families of operators P_h, depending on a geometric or mechanical
parameter h, that approaches the identity as h goes to 0. It is shown that (P_h
-I)/h converges for small h to a second order elliptic differential operator L
on compactly supported functions and that the Markov chain process associated
to P_h converges to a diffusion with infinitesimal generator L. Both P_h and L
are selfadjoint (densely) defined on the space L2(H,{\eta}) of
square-integrable functions over the (lower) half-space H in R^m, where {\eta}
is a stationary measure. This measure's density is either (post-collision)
Maxwell-Boltzmann distribution or Knudsen cosine law, and the random processes
with infinitesimal generator L respectively correspond to what we call MB
diffusion and (generalized) Legendre diffusion. Concrete examples of simple
mechanical systems are given and illustrated by numerically simulating the
random processes.Comment: 34 pages, 13 figure
Vortex states in nanoscale superconducting squares: the influence of quantum confinement
Bogoliubov-de Gennes theory is used to investigate the effect of the size of
a superconducting square on the vortex states in the quantum confinement
regime. When the superconducting coherence length is comparable to the Fermi
wavelength, the shape resonances of the superconducting order parameter have
strong influence on the vortex configuration. Several unconventional vortex
states, including asymmetric ones, giant multi-vortex combinations, and states
comprising giant antivortex, were found as ground states and their stability
was found to be very sensitive on the value of , the size of the
sample , and the magnetic flux . By increasing the temperature and/or
enlarging the size of the sample, quantum confinement is suppressed and the
conventional mesoscopic vortex states as predicted by the Ginzburg-Laudau (GL)
theory are recovered. However, contrary to the GL results we found that the
states containing symmetry-induced vortex-antivortex pairs are stable over the
whole temperature range. It turns out that the inhomogeneous order parameter
induced by quantum confinement favors vortex-antivortex molecules, as well as
giant vortices with a rich structure in the vortex core - unattainable in the
GL domain
Half-skyrmion picture of single hole doped CuO_2 plane
Based on the Zhang-Rice singlet picture, it is argued that the half-skyrmion
is created by the doped hole in the single hole doped high-T_c cuprates with
N'eel ordering. The spin configuration around the Zhang-Rice singlet, which has
the form of superposition of the two different d-orbital hole spin states, is
studied within the non-linear \sigma model and the CP^1 model. The spin
configurations associated with each hole spin state are obtained, and we find
that the superposition of these spin configuration turns out to be the
half-skyrmion that is characterized by a half of the topological charge. The
excitation spectrum of the half-skyrmion is obtained by making use of Lorentz
invariance of the effective theory and is qualitatively in good agreement with
angle resolved photoemission spectroscopy on the parent compunds. Estimated
values of the parameters contained in the excitation spectrum are in good
agreement with experimentally obtained values. The half-skyrmion theory
suggests a picture for the difference between the hole doped compounds and the
electron doped compounds.Comment: 13 pages, 2 figures, to be published in Phys. Rev.
Topology of modified helical gears
The topology of several types of modified surfaces of helical gears is proposed. The modified surfaces allow absorption of a linear or almost linear function of transmission errors. These errors are caused by gear misalignment and an improvement of the contact of gear tooth surfaces. Principles and corresponding programs for computer aided simulation of meshing and contact of gears have been developed. The results of this investigation are illustrated with numerical examples
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