Rectification in one--dimensional electronic systems

Asymmetric current--voltage ($I(V)$) curves, known as the diode or rectification effect, in one--dimensional electronic conductors can have their origin from scattering off a single asymmetric impurity in the system. We investigate this effect in the framework of the Tomonaga--Luttinger model for electrons with spin. We show that electron interactions strongly enhance the diode effect and lead to a pronounced current rectification even if the impurity potential is weak. For strongly interacting electrons and not too small voltages, the rectification current, $I_r = [I(V)+I(-V)]/2$, measuring the asymmetry in the current--voltage curve, has a power--law dependence on the voltage with a negative exponent, $I_r \sim V^{-|z|}$, leading to a bump in the current--voltage curve.Comment: 9 pages; 3 figure

Magnetic impurity coupled to interacting conduction electrons

We consider a magnetic impurity which interacts by hybridization with a system of weakly correlated electrons and determine the energy of the ground state by means of an 1/N_f expansion. The correlations among the conduction electrons are described by a Hubbard Hamiltonian and are treated to lowest order in the interaction strength. We find that their effect on the Kondo temperature, T_K, in the Kondo limit is twofold: First, the position of the impurity level is shifted due to the reduction of charge fluctuations, which reduces T_K. Secondly, the bare Kondo exchange coupling is enhanced as spin fluctuations are enlarged. In total, T_K increases. Both corrections require intermediate states beyond the standard Varma-Yafet ansatz. This shows that the Hubbard interaction does not just provide quasiparticles, which hybridize with the impurity, but also renormalizes the Kondo coupling.Comment: ReVTeX 19 pages, 3 uuenconded postscript figure

N\'eel transition, spin fluctuations, and pseudogap in underdoped cuprates by a Lorentz invariant four-fermion model in 2+1 dimensions

We show that the N\'eel transition and spin fluctuations near the N\'eel transition in planar cuprates can be described by an SU(2) invariant relativistic four-fermion model in 2+1 dimensions. Features of the pseudogap phenomenon are naturally described by the appearance of an anomalous dimension for the spinon propagator.Comment: 5 pages, 2 figures (revtex4). Final revised and corrected versio

Parametric study of prospective early commercial MHD power plants (PSPEC). General Electric Company, task 1: Parametric analysis

The performance and cost of moderate technology coal-fired open cycle MHD/steam power plant designs which can be expected to require a shorter development time and have a lower development cost than previously considered mature OCMHD/steam plants were determined. Three base cases were considered: an indirectly-fired high temperature air heater (HTAH) subsystem delivering air at 2700 F, fired by a state of the art atmospheric pressure gasifier, and the HTAH subsystem was deleted and oxygen enrichment was used to obtain requisite MHD combustion temperature. Coal pile to bus bar efficiencies in ease case 1 ranged from 41.4% to 42.9%, and cost of electricity (COE) was highest of the three base cases. For base case 2 the efficiency range was 42.0% to 45.6%, and COE was lowest. For base case 3 the efficiency range was 42.9% to 44.4%, and COE was intermediate. The best parametric cases in bases cases 2 and 3 are recommended for conceptual design. Eventual choice between these approaches is dependent on further evaluation of the tradeoffs among HTAH development risk, O2 plant integration, and further refinements of comparative costs

Duality relations and exotic orders in electronic ladder systems

We discuss duality relations in correlated electronic ladder systems to clarify mutual relations between various conventional and unconventional phases. For the generalized two-leg Hubbard ladder, we find two exact duality relations, and also one asymptotic relation which holds in the low-energy regime. These duality relations show that unconventional (exotic) density-wave orders such as staggered flux or circulating spin-current are directly mapped to conventional density-wave orders, which establishes the appearance of various exotic states with time-reversal and/or spin symmetry breaking. We also study duality relations in the SO(5) symmetry that was proposed to unify antiferromagnetism and d-wave superconductivity. We show that the same SO(5) symmetry also unifies circulating spin current order and s-wave superconductivity.Comment: 9 pages, 2 figures; Proceedings of SPQS2004 (Sendai

3-D Photoionization Structure and Distances of Planetary Nebulae II. Menzel 1

We present the results of a spatio-kinematic study of the planetary nebula Menzel 1 using spectro-photometric mapping and a 3-D photoionization code. We create several 2-D emission line images from our long-slit spectra, and use these to derive the line fluxes for 15 lines, the Halpha/Hbeta extinction map, and the [SII] line ratio density map of the nebula. We use our photoionization code constrained by these data to derive the three-dimensional nebular structure and ionizing star parameters of Menzel 1 by simultaneously fitting the integrated line intensities, the density map, and the observed morphologies in several lines, as well as the velocity structure. Using theoretical evolutionary tracks of intermediate and low mass stars, we derive a mass for the central star of 0.63+-0.05 Msolar. We also derive a distance of 1050+_150 pc to Menzel 1.Comment: To be published in ApJ of 10th February 2005. 12 figure

High Resolution Infrared Imaging and Spectroscopy of the Pistol Nebula: Evidence for Ejection

We present new NICMOS/HST infrared images and CGS4/UKIRT Br-alpha (4.05 um) spectroscopy of the Pistol Star and its associated nebula, finding strong evidence to support the hypothesis that the Pistol Nebula was ejected from the Pistol Star. The Pa-alpha NICMOS image shows that the nebula completely surrounds the Pistol Star, although the line intensity is much stronger on its northern and western edges. The Br-alpha spectra show the classical ring-like signature of quasi-spherical expansion, with weak blueshifted emission (V_max approx -60 km/s) and strong redshifted emission (V_max approx +10 km/s), where the velocities are with respect to the velocity of the Pistol Star; further, the redshifted emission appears to be "flattened" in the position-velocity diagram. These data suggest that the nebula was ejected from the star several thousand years ago, with a velocity between the current terminal velocity of the stellar wind (95 km/s) and the present expansion velocity of gas in the outer shell of the nebula (60 km/s). The Pa-alpha image reveals several emission-line stars in the region, including two newly-identified emission-line stars north of the Pistol Star with spectral types earlier than WC8 (T_eff > 50,000 K). The presence of these stars, the morphology of the Pa-alpha emission, and the velocity field in the gas suggest that the side of the nebula furthest from us is approaching, and being ionized by, the hot stars of the Quintuplet, and that the highest velocity redshifted gas has been decelerated by winds from the Quintuplet stars. We also discuss the possibility that the nebular gas might be magnetically confined by the ambient magnetic field delineated by the nearby nonthermal filaments.Comment: Figure 1 is included as a JPG file. Figure 1 and 2 also available at ftp://quintup.astro.ucla.edu/pistol2

Staggered orbital currents in the half-filled two-leg ladder

Using Abelian bosonization with a careful treatment of the Klein factors, we show that a certain phase of the half-filled two-leg ladder, previously identified as having spin-Peierls order, instead exhibits staggered orbital currents with no dimerization.Comment: 8 pages, 2 figures. Final versio

Charge pairing, superconducting transition and supersymmetry in high-temperature cuprate superconductors

We propose a model for high-T$_{c}$ superconductors, valid for $0\leq\delta\leq\delta_{SC}$, that includes both the spin fluctuations of the Cu$^{++}$ magnetic ions and of the O$^{--}$ doped holes. Spin-charge separation is taken into account with the charge of the doped holes being associated to quantum skyrmion excitations (holons) of the Cu$^{++}$ spin background. The holon effective interaction potential is evaluated as a function of doping, indicating that Cooper pair formation is determined by the competition between the spin fluctuations of the Cu$^{++}$ background and of spins of the O$^{--}$ doped holes (spinons). The superconducting transition occurs when the spinon fluctuations dominate, thereby reversing the sign of the interaction. At this point ($\delta = \delta_{SC}$), the theory is supersymmetric at short distances and, as a consequence, the leading order results are not modified by radiative corrections. The critical doping parameter for the onset of superconductivity at T=0 is obtained and found to be a universal constant determined by the shape of the Fermi surface. Our theoretical values for $\delta_{SC}$ are in good agreement with the experiment for both LSCO and YBCO.Comment: RevTex, 4 pages, no figure

Nonlinear Modes of Liquid Drops as Solitary Waves

The nolinear hydrodynamic equations of the surface of a liquid drop are shown to be directly connected to Korteweg de Vries (KdV, MKdV) systems, giving traveling solutions that are cnoidal waves. They generate multiscale patterns ranging from small harmonic oscillations (linearized model), to nonlinear oscillations, up through solitary waves. These non-axis-symmetric localized shapes are also described by a KdV Hamiltonian system. Recently such ``rotons'' were observed experimentally when the shape oscillations of a droplet became nonlinear. The results apply to drop-like systems from cluster formation to stellar models, including hyperdeformed nuclei and fission.Comment: 11 pages RevTex, 1 figure p