328,243 research outputs found
Resonant Raman scattering of quantum wire in strong magnetic field
The resonant Raman scattering of a quantum wire in a strong magnetic field is
studied, focused on the effect of long range Coulomb interaction and the
spin-charge separation. The energy-momentum dispersions of charge and spin
excitation obtained from Raman cross-section show the characteristc cross-over
behaviour induced by inter-edge Coulomb interaction. The "SPE" peak near
resonance in polarized spectra becomes broad due to the momentum dependence of
charge velocity. The broad peak in the depolarized spectra is shown to
originate from the disparity between charge and spin excitation velocity.Comment: RevTex file, 6 pages, no figure: To appear in Int. Jour. Mod. Phys.
Theoretical analysis of spectral gain in a THz quantum cascade laser: prospects for gain at 1 THz
In a recent Letter [Appl. Phys. Lett. 82, 1015 (2003)], Williams et al.
reported the development of a terahertz quantum cascade laser operating at 3.4
THz or 14.2 meV. We have calculated and analyzed the gain spectra of the
quantum cascade structure described in their work, and in addition to gain at
the reported lasing energy of ~= 14 meV, we have discovered substantial gain at
a much lower energy of around 5 meV or just over 1 THz. This suggests an avenue
for the development of a terahertz laser at this lower energy, or of a
two-color terahertz laser.Comment: in press APL, tentative publication date 29 Sep 200
Direct transmission of pictorial information in multimode optical fibers
The problem of coherent image transmission through a single multimode optical fiber is discussed. A scheme is presented for recovering the transmitted image after distortions brought about by the fiber modes dispersion. Realization of this scheme by holographic techniques and with lens systems is proposed, and its limitations pointed out. The application of this scheme in canceling out temporal signal dispersion in a multimode fiber transmission line is also discussed briefly
Topological Superconductivity and Majorana Fermions in Metallic Surface-States
Heavy metals, such as Au, Ag, and Pb, often have sharp surface states that
are split by strong Rashba spin-orbit coupling. The strong spin-orbit coupling
and two-dimensional nature of these surface states make them ideal platforms
for realizing topological superconductivity and Majorana fermions. In this
paper, we further develop a proposal to realize Majorana fermions at the ends
of quasi-one-dimensional metallic wires. We show how superconductivity can be
induced on the metallic surface states by a combination of proximity effect,
disorder, and interactions. Applying a magnetic field along the wire can drive
the wire into a topologically non-trivial state with Majorana end-states.
Unlike the case of a perpendicular field, where the chemical potential must be
fined tuned near the Rashba-band crossing, the parallel field allows one to
realize Majoranas for arbitrarily large chemical potential. We then show that,
despite the presence of a large carrier density from the bulk metal, it is
still possible to effectively control the chemical potential of the surface
states by gating. The simplest version of our proposal, which involves only an
Au(111) film deposited on a conventional superconductor, should be readily
realizable.Comment: 9 Pages, 6 Figure
Ectoparasitic Arthropods Collected From Some Northern Ohio Mammals
Ectoparasitic arthropods were collected from some fur-bearing mammals in northern Ohio. Specimens representing seven mammalian species were examined and found to collectively harbor acarines, fleas, and biting lice. Species determinations were made and new host and state records noted
Quantitative absorption and fluorescence studies of NO between 1060 and 2000 A
Synchrotron radiation in the 1060 to 2000 A region was used to measure the average absorption and fluorescence cross sections of NO and to determine approximate photodissociation quantum yields. Several vibrational levels of the D(2) sigma(+), E(2) sigma(+), and B(2) delta states have high fluorescence quantum yields. The C(2) and B(2) states do not fluoresce when the excitation energies are above the first dissociation limit, in accord with previous experiments. In general, the fluorescence yields decrease with increasing photon energy. The quantitative measurements are compared with spectroscopic observations and are found to be reasonably consistent
An economical vent cover
Inexpensive formed-plastic vent cover has been developed that allows controlled purge of vent systems and also provides blowout protection. Cover can also be used in relief mode to allow normal system relief flows without disengaging from vent system. Cover consists of two parts made of plastics with varying densities to fit media used and desired pressures
Engineering a p+ip Superconductor: Comparison of Topological Insulator and Rashba Spin-Orbit Coupled Materials
We compare topological insulator materials and Rashba coupled surfaces as
candidates for engineering p+ip superconductivity. Specifically, in each type
of material we examine 1) the limitations to inducing superconductivity by
proximity to an ordinary s-wave superconductor, and 2) the robustness of the
resulting superconductivity against disorder. We find that topological
insulators have strong advantages in both regards: there are no fundamental
barriers to inducing superconductivity, and the induced superconductivity is
immune to disorder. In contrast, for Rashba coupled quantum wires or surface
states, the the achievable gap from induced superconductivity is limited unless
the Rashba coupling is large. Furthermore, for small Rashba coupling the
induced superconductivity is strongly susceptible to disorder. These features
pose serious difficulties for realizing p+ip superconductors in semiconductor
materials due to their weak spin-orbit coupling, and suggest the need to seek
alternatives. Some candidate materials are discussed.Comment: 10 pages, 4 Figures; Changes for v2: References added, Includes an
expanded discussion of surface vs bulk disorder (see Sec. IVc. and Appendix
A
Development of EHD Ion-Drag Micropump for Microscale Electronics Cooling Systems
In this investigation, the numerical simulation of electrohydrodynamic (EHD)
ion-drag micropumps with micropillar electrode geometries have been performed.
The effect of micropillar height and electrode spacing on the performance of
the micropumps was investigated. The performance of the EHD micropump improved
with increased applied voltage and decreased electrode spacing. The optimum
micropillar height for the micropump with electrode spacing of 40m and
channel height of 100m at 200V was 40m, where a maximum mass flow
rate of 0.18g/min was predicted. Compared to that of planar electrodes, the 3D
micropillar electrode geometry enhanced the overall performance of the EHD
micropumps.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
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