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

Multichannel Generalization of Kitaev's Majorana End States and a Practical Route to Realize Them in Thin Films

The ends of one-dimensional p+ip superconductors have long been predicted to possess localized Majorana fermion modes. We show that Majorana end states survive beyond the strict 1D single-channel limit so long as the sample width does not exceed the superconducting coherence length, and exist when an odd number of transverse quantization channels are occupied. Consequently we find that the system undergoes a sequence of topological phase transitions driven by changing the chemical potential. These observations make it feasible to implement quasi-1D p+ip superconductors in metallic thin-film microstructures, which offer 3-4 orders of magnitude larger energy scales than semiconductor-based schemes. Some promising candidate materials are described.Comment: 5 pages, 5 figures, final published version, appendix on samples with random edge geometries adde