Lower Bound for the Fermi Level Density of States of a Disordered D-Wave Superconductor in Two Dimensions

We consider a disordered d--wave superconductor in two dimensions. Recently, we have shown in an exact calculation that for a lattice model with a Lorentzian distributed random chemical potential the quasiparticle density of states at the Fermi level is nonzero. As the exact result holds only for the special choice of the Lorentzian, we employ different methods to show that for a large class of distributions, including the Gaussian distribution, one can establish a nonzero lower bound for the Fermi level density of states. The fact that the tails of the distributions are unimportant in deriving the lower bound shows that the exact result obtained before is generic.Comment: 15 preprint pages, no figures, submitted to PR

Optical Hall conductivity of systems with gapped spectral nodes

We calculate the optical Hall conductivity within the Kubo formalism for systems with gapped spectral nodes, where the latter have a power-law dispersion with exponent n. The optical conductivity is proportional to n and there is a characteristic logarithmic singularity as the frequency approaches the gap energy. The optical Hall conductivity is almost unaffected by thermal fluctuations and disorder for n=1, whereas disorder has a stronger effect on transport properties if n=2

The effects of Zn Impurity on the Properties of Doped Cuprates in the Normal State

We study the interplay of quantum impurity, and collective spinon and holon dynamics in Zn doped high-T$_c$ cuprates in the normal state. The two-dimensional t-t$^{\prime}$-J models with one and a small amount of Zn impurity are investigated within a numerical method based on the double-time Green function theory. We study the inhomogeneities of holon density and antiferromagnetic correlation background in cases with different Zn concentrations, and obtain that doped holes tend to assemble around the Zn impurity with their mobility being reduced. Therefore a bound state of holon is formed around the nonmagnetic Zn impurity with the effect helping Zn to introduce local antiferromagnetism around itself. The incommensurate peaks we obtained in the spin structure factor indicate that Zn impurities have effects on mixing the q=($\pi$, $\pi$) and q=0 components in spin excitations.Comment: 5 pages, 3 figure

Subsonic longitudinal and lateral-directional static aerodynamic characteristics of a general research fighter configuration employing a jet sheet vortex generator

A configuration concept for developing vortex lift, which replaces the physical wing strake with a jet sheet generated fluid strake, was investigated on a general research fighter model. The vertical and horizontal location of the jet sheet with respect to the wing leading edge was studied over a momentum coefficient range from 0 to 0.24 in the Langley 7- by 10-foot high speed tunnel over a Mach number range from 0.3 to 0.8. The angle of attack range studied was from -2 to 30 deg at sideslip angles of 0, -5, and 5 deg. Test data are presented without analysis

Bose-Einstein Quantum Phase Transition in an Optical Lattice Model

Bose-Einstein condensation (BEC) in cold gases can be turned on and off by an external potential, such as that presented by an optical lattice. We present a model of this phenomenon which we are able to analyze rigorously. The system is a hard core lattice gas at half-filling and the optical lattice is modeled by a periodic potential of strength $\lambda$. For small $\lambda$ and temperature, BEC is proved to occur, while at large $\lambda$ or temperature there is no BEC. At large $\lambda$ the low-temperature states are in a Mott insulator phase with a characteristic gap that is absent in the BEC phase. The interparticle interaction is essential for this transition, which occurs even in the ground state. Surprisingly, the condensation is always into the $p=0$ mode in this model, although the density itself has the periodicity of the imposed potential.Comment: RevTeX4, 13 pages, 2 figure

Discussion of the Electromotive Force Terms in the Model of Parker-unstable Galactic Disks with Cosmic Rays and Shear

We analyze the electromotive force (EMF) terms and basic assumptions of the linear and nonlinear dynamo theories in our three-dimensional (3D) numerical model of the Parker instability with cosmic rays and shear in a galactic disk. We also apply the well known prescriptions of the EMF obtained by the nonlinear dynamo theory (Blackman & Field 2002 and Kleeorin et al. 2003) to check if the EMF reconstructed from their prescriptions corresponds to the EMF obtained directly from our numerical models. We show that our modeled EMF is fully nonlinear and it is not possible to apply any of the considered nonlinear dynamo approximations due to the fact that the conditions for the scale separation are not fulfilled.Comment: 15 pages, 12 figure

Characterization of the Local Density of States Fluctuations near the Integer Quantum Hall Transition in a Quantum Dot Array

We present a calculation for the second moment of the local density of states in a model of a two-dimensional quantum dot array near the quantum Hall transition. The quantum dot array model is a realistic adaptation of the lattice model for the quantum Hall transition in the two-dimensional electron gas in an external magnetic field proposed by Ludwig, Fisher, Shankar and Grinstein. We make use of a Dirac fermion representation for the Green functions in the presence of fluctuations for the quantum dot energy levels. A saddle-point approximation yields non-perturbative results for the first and second moments of the local density of states, showing interesting fluctuation behaviour near the quantum Hall transition. To our knowledge we discuss here one of the first analytic characterizations of chaotic behaviour for a two-dimensional mesoscopic structure. The connection with possible experimental investigations of the local density of states in the quantum dot array structures (by means of NMR Knight-shift or single-electron-tunneling techniques) and our work is also established.Comment: 11 LaTeX pages, 1 postscript figure, to appear in Phys.Rev.

Origin of magnetic moments in defective TiO2 single crystals

In this paper we show that ferromagnetism can be induced in pure TiO2 single crystals by oxygen ion irradiation. By combining x-ray diffraction, Raman-scattering, and electron spin resonance spectroscopy, a defect complex, \emph{i.e.} Ti$^{3+}$ ions on the substitutional sites accompanied by oxygen vacancies, has been identified in irradiated TiO2. This kind of defect complex results in a local (TiO$_{6-x}$) stretching Raman mode. We elucidate that Ti$^{3+}$ ions with one unpaired 3d electron provide the local magnetic moments.Comment: 4 pages, 4 figures, to be published at Phys. Rev.