May 1998 arXiv papers — page 20

W. Henderson, M. J. Higgins, E. Y. Andrei

We have measured the response of the flux-line lattice in the low T$_c$ superconductor, 2H-NbSe$_2$, to finite frequency drives. In a well-defined range of fields, temperatures, and driving amplitudes the system exhibits a variety of novel non-linear phenomena. Most strikingly, the flux-lines can move easily in response to currents that are significantly low

Ph. Ghosez, J. P. Michenaud, X. Gonze

Based on recent first-principles computations in perovskite compounds, especially BaTiO3, we examine the significance of the Born effective charge concept and contrast it with other atomic charge definitions, either static (Mulliken, Bader...) or dynamical (Callen, Szigeti...). It is shown that static and dynamical charges are not driven by the same underlyi

Ph. Ghosez, X. Gonze

The Born effective charge, Z*, that describes the polarization created by collective atomic displacements, can be computed from first-principles by different techniques. Its band-by-band decomposition appeared recently as a powerful tool for the microscopic characterisation of the bonding in solids. We describe the connections between the different expressio

Louis Felix Feiner, Andrzej M. Oles

We derive a spin-orbital model for insulating LaMnO_3 which fulfills the SU(2) symmetry of S=2 spins at Mn^{3+} ions. It includes the complete e_g and t_{2g} superexchange which follows from a realistic Mn^{2+} multiplet structure in cubic site symmetry, and the Jahn-Teller induced orbital interactions. We show that the magnetic ordering observed in LaMnO_3

David Lancaster, Theo Nieuwenhuizen

The disturbance of the transmission of light through a diffusive medium due to an object hidden in it can be expressed in terms of an effective charge and dipole moment. In the mesoscopic regime, beyond the diffusion approximation, we calculate this effective charge and dipole moment. Various objects are considered: a single point scatterer, a localised dens

Yoshio Kuramoto

The poor man's scaling is extended to higher order by the use of the open-shell Rayleigh-Schroedinger perturbation theory. A generalized Kondo-type model with the SU(n) times SU(m) symmetry is proposed and renormalized to the third order. It is shown that the model has both local Fermi-liquid and non-Fermi-liquid fixed points, and that the latter becomes

K. Reuter, P. L. de Andres, F. J. Garcia-Vidal, D. Sestovic

We present a Green's function approach based on a LCAO scheme to compute the elastic propagation of electrons injected from a STM tip into a metallic film. The obtained 2D current distribution in real and reciprocal space furnish a good representation of the elastic component of Ballistic Electron Emission Microscopy (BEEM) currents. Since this component

K. Reuter, P. L. de Andres, F. J. Garcia-Vidal, F. Flores

Using a Green's function approach, we investigate band structure effects in the BEEM current distribution in reciprocal space. In the elastic limit, this formalism provides a 'parameter free' solution to the BEEM problem. At low temperatures, and for thin metallic layers, the elastic approximation is enough to explain the experimental I(V) curves

Maxim Ershov

Lateral physical effects in single quantum well infrared photodetectors (SQWIPs) under non-uniform illumination over detector area are considered. These effects are due mainly to the in-plane transport of the photoinduced charge in the QW. The length of the lateral photocurrent spreading is determined by the in-plane conductivity of the carriers in the QW an

Chinmay Das, H. R. Krishnamurthy

We have studied the ordering of a two dimensional charge stabilised colloidal system in the presence of a stationary one dimensionally modulated laser field formed by the superposition of two modulations with wavevectors $q_0 τ$ and $q_0/τ$, where $q_0$ is the wavevector corresponding to the first peak of the direct correlation function of the unperturbed li

Hirokazu Tsunetsugu, Masatoshi Imada

Drude weight of optical conductivity is calculated at zero temperature by exact diagonalization for the two-dimensional t-J model with the two-particle term, $W$. For the ordinary t-J model with $W$=0, the scaling of the Drude weight $D \propto δ^2$ for small doping concentration $δ$ is obtained, which indicates anomalous dynamic exponent $z$=4 of the Mott t

N. A. Levenson, James R. Graham, Luke D. Keller, Matthew J. Richter

We present a complete atlas of the Cygnus Loop supernova remnant in the light of [O III] (5007), H alpha, and [S II] (6717, 6731). Despite its shell-like appearance, the Cygnus Loop is not a current example of a Sedov-Taylor blast wave. Rather, the optical emission traces interactions of the supernova blast wave with clumps of gas. The surrounding interstell

M. Coleman Miller, Frederick K. Lamb, Gregory B. Cook

Quasi-periodic X-ray brightness oscillations (QPOs) with frequencies around a kilohertz have now been discovered in more than a dozen neutron stars in low-mass X-ray binary systems using the Rossi X-ray Timing Explorer. There is strong evidence that the frequencies of the kilohertz oscillations are the orbital frequencies of accreting gas in nearly circular

A. N. Witt, K. D. Gordon, D. G. Furton

We have reviewed the characteristics of the extended red emission (ERE) as observed in many dusty astronomical environments, in particular, the diffuse interstellar medium of the Galaxy. The spectral nature and the photon conversion efficiency of the ERE identify the underlying process as highly efficient photoluminescence by an abundant component of interst

E. Pian, A. Koratkar, L. Maraschi, C. M. Urry

Archival IUE SWP and HST FOS spectra show the presence of a relatively strong, broad Lyman alpha emission line superposed onto the UV spectral continuum of the blazar 3C 279. As opposed to a factor ~50 variation of the continuum flux during eight years, the emission line did not exhibit significant intensity changes. Simultaneous IUE SWP and LWP spectra of 3

Laura Maraschi

The IUE contribution to the understanding of the blazar phenomenon has been of fundamental importance. Here I review the progress obtained with the latest multifrequency campaigns performed with IUE on two prototype objects, the BL Lac PKS 2155-304 and the highly polarized, superluminal quasar 3C 279.

Z. Ivezic, G. R. Knapp, M. Elitzur

We present a detailed, self-consistent model of radiatively driven stellar outflows which couples the radiative transfer and hydrodynamics equations. The circumstellar envelope, which consists of gas and dust, is described as a two-component fluid to account for relative drifts. Our results agree with both molecular line observations and infrared continuum s

D. B. Melrose, J. -P. Macquart

Different ray paths through a turbulent plasma can produce stochastic Faraday rotation leading to depolarization of any linearly polarized component. Simple theory predicts that the average values of the Stokes parameters decay according to $<Q>$, $<U>\propto\exp(-δ_l)$, with $δ_l\proptoλ^4$. It is pointed out that a definitive test for such depolarization i

A. S. Bhattal, N. Francis, S. J. Watkins, A. P. Whitworth

A Lagrangian, particle-based numerical method (tree code gravity plus smoothed particle hydrodynamics) was used to simulate clump-clump collisions occurring within GMCs. The collisions formed shock-compressed layers, out of which condensed approximately co-planar protostellar discs of 7-60 solar masses and 500-1000AU radius. Binary and multiple systems were