Elastic forward scattering in the cuprate superconducting state

We investigate the effect of elastic forward scattering on the ARPES spectrum of the cuprate superconductors. In the normal state, small angle scattering from out-of-plane impurities is thought to broaden the ARPES spectral response with minimal effect on the resistivity or the superconducting transition temperature $T_c$. Here we explore how such forward scattering affects the ARPES spectrum in the d-wave superconducting state. Away from the nodal direction, the one-electron impurity scattering rate is found to be suppressed as $\omega$ approaches the gap edge by a cancellation between normal and anomalous scattering processes, leading to a square-root-like feature in the spectral weight as $\omega$ approaches -\Delta_\k from below. For momenta away from the Fermi surface, our analysis suggests that a dirty optimally or overdoped system will still display a sharp but nondispersive peak which could be confused with a quasiparticle spectral feature. Only in cleaner samples should the true dispersing quasiparticle peak become visible. At the nodal point on the Fermi surface, the contribution of the anomalous scattering vanishes and the spectral weight exhibits a Lorentzian quasiparticle peak in both energy and momentum. Our analysis, including a treatment of unitary scatterers and inelastic spin fluctuation scattering, suggests explanations for the sometimes mysterious lineshapes and temperature dependences of the peak structures observed in the \BSCCO system.Comment: 12 pages, 14 figure

Negative Giant Longitudinal Magnetoresistance in NiMnSb/InSb: An interface effect

We report on the electrical and magneto-transport properties of the contact formed between polycrystalline NiMnSb thin films grown using pulsed laser deposition (PLD) and n-type degenerate InSb (100) substrates. A negative giant magnetoresistance (GMR) effect is observed when the external magnetic field is parallel to the surface of the film and to the current direction. We attribute the observed phenomenon to magnetic precipitates formed during the magnetic film deposition and confined to a narrow layer at the interface. The effect of these precipitates on the magnetoresistance depends on the thermal processing of the system.Comment: 14 pages, 4 figure

C-axis Josephson Tunneling Between YBCO and Pb: Direct Evidence for Mixed Order Parameter Symmetry in a High-T_c Superconductor

We report a new class of $c$-axis Josephson tunneling experiments in which a conventional superconductor (Pb) is deposited across a single twin boundary of a YBa_2Cu_3O_{7-\delta} crystal. We measure the critical current as a function of magnitude and angle of magnetic field applied in the plane of the junction. In all samples, we observe a clear experimental signature of an order parameter phase shift across the twin boundary. These results provide strong evidence for mixed $d$- and $s$-wave pairing in YBCO, with a reversal in the sign of the $s$-wave component across the twin boundary.Comment: 4 pages RevTex, 4 postscript figures included, submitted to Phys. Rev. Let

Surface and interface study of pulsed-laser-deposited off-stoichiometric NiMnSb thin films on Si(100) substrate

We report a detailed study of surface and interface properties of pulsed-laser deposited NiMnSb films on Si (100) substrate as a function of film thickness. As the thickness of films is reduced below 35 nm formation of a porous layer is observed. Porosity in this layer increases with decrease in NiMnSb film thickness. These morphological changes of the ultra thin films are reflected in the interesting transport and magnetic properties of these films. On the other hand, there are no influences of compositional in-homogeneity and surface/interface roughness on the magnetic and transport properties of the films.Comment: 13 pages, 7 figures, Submitted to Phys. Rev.

A comparative study of the magnetic and magnetotransport properties between a metallic (x=0.6) and a semiconducting (x=0.2) member of the solid solution LaNixCo1-xO3

We present a comparative study of both the magnetic and magnetotransport properties for two members of the perovskite solid solution LaNixCo1-xO3 (x=0.2, 0.6) located on opposite sides of the chemically induced metal-to-insulator transition. LaNi0.6Co0.4O3 exhibits metallic behavior and small but negative magnetoresistance, whereas LaNi0.2Co0.8O3 exhibits semiconducting behavior and giant negative magnetoresistance at low temperatures. On the other hand, we observe pronounced similarities in the magnetic properties of both compounds. A consistent explanation regarding the origin of the magnetoresistance in the two members of the solid solution is provided.Comment: 29 pages, 10 figures, pdf forma

Magnetic-interference patterns in Josephson junctions with d+is symmetry

The magnetic interference pattern and the spontaneous flux in unconventional Josephson junctions of superconductors with d+is symmetry are calculated for different reduced junction lengths and the relative factor of the d and s wave components. This is a time reversal broken symmetry state. We study the stability of the fractional vortex and antivortex which are spontaneously formed and examine their evolution as we change the length and the relative factor of d and s wave components. The asymmetry in the field modulated diffraction pattern exists for lengths as long as L=10\lambda_J.Comment: 8 pages, 6 eps files, submitted to PR