26,307 research outputs found
Tunneling into the normal state of Pr(2-x)CexCuO4
The temperature dependence of the tunneling conductance was measured for
various doping levels of Pr(2-x)CexCuO4 using planar junctions. A normal state
gap is seen at all doping levels studied, x=0.11 to x=0.19. We find it to
vanish above a certain temperature T*. T* is greater than Tc for the underdoped
region and it follows Tc on the overdoped side. This behavior suggests finite
pairing amplitude above Tc on the underdoped side
Effects of annealing and strain on La_{1-x}Ca_{x}MnO_{3} thin films: a new phase diagram in the ferromagnetic region
Oriented, single phase thin films of La_{1-x}Ca_{x}MnO_{3} have been
deposited onto (100)-oriented LaAlO_{3} (0.1<x<0.5) substrates using the Pulsed
Laser Deposition technique. While for some compositions the physical properties
(transport and magnetization) of the as-grown films are higher than the bulk
values, for other calcium contents the optimized properties are obtained only
after annealing under oxygen. These data can be partly explained by changes in
oxygen content, resulting in cationic vacancies and thus self-doping effects -
accompanying structural changes, may be the cause of properties beyond the
phase diagram. We propose a new phase diagram for
(La_{1-x}Ca_{x})_{1-y}\square_{y}MnO_{3} (0.1<x<0.5) thin films.Comment: 8 pages, 5 figures submitted to Applied Physics Letter
Optimization of the Ballistic Guide Design for the SNS FNPB 8.9 A Neutron Line
The optimization of the ballistic guide design for the SNS Fundamental
Neutron Physics Beamline 8.9 A line is described. With a careful tuning of the
shape of the curve for the tapered section and the width of the straight
section, this optimization resulted in more than 75% increase in the neutron
flux exiting the 33 m long guide over a straight m=3.5 guide with the same
length.Comment: 21 pages, 13 figures; added a paragraph on existing ballistic guides
to respond to referee comments; accepted for publication in Nuclear Inst. and
Methods in Physics Research,
The effect of substrate induced strain on the charge-ordering transition in Nd_{0.5}Sr_{0.5}MnO_{3} thin films
We report the synthesis and characterization of Nd_{0.5}Sr_{0.5}MnO_{3} thin
films grown by the Pulsed Laser Deposition technique on 100 -oriented LaAlO_{3}
substrates. X-ray diffraction (XRD) studies show that the films are 101
-oriented, with a strained and quasi-relaxed component, the latter increasing
with film thickness. We observe that transport properties are strongly
dependent on the thickness of the films. Variable temperature XRD down to 100 K
suggests that this is caused by substrate induced strain on the films.Comment: 3 pages REVTeX, 4 figures included, submitted to AP
Exciton-magnon effects in the optical spectrum of MnF2
Exciton and magnon absorption, emission spectra, and fluorescence of antiferromagnetic manganese fluorid
Steep-Spectrum Radio Emission from the Low-Mass Active Galactic Nucleus GH 10
GH 10 is a broad-lined active galactic nucleus (AGN) energized by a black
hole of mass 800,000 Solar masses. It was the only object detected by Greene et
al. in their Very Large Array (VLA) survey of 19 low-mass AGNs discovered by
Greene & Ho. New VLA imaging at 1.4, 4.9, and 8.5 GHz reveals that GH 10's
emission has an extent of less than 320 pc, has an optically-thin synchrotron
spectrum with a spectral index -0.76+/-0.05, is less than 11 percent linearly
polarized, and is steady - although poorly sampled - on timescales of weeks and
years. Circumnuclear star formation cannot dominate the radio emission, because
the high inferred star formation rate, 18 Solar masses per year, is
inconsistent with the rate of less than 2 Solar masses per year derived from
narrow Halpha and [OII] 3727 emission. Instead, the radio emission must be
mainly energized by the low-mass black hole. GH 10's radio properties match
those of the steep-spectrum cores of Palomar Seyfert galaxies, suggesting that,
like those Seyferts, the emission is outflow-driven. Because GH 10 is radiating
close to its Eddington limit, it may be a local analog of the starting
conditions, or seeds, for supermassive black holes. Future imaging of GH 10 at
higher resolution thus offers an opportunity to study the relative roles of
radiative versus kinetic feedback during black-hole growth.Comment: 7 pages; 2 figures; emulateapj; to appear in Ap
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Normal State Nernst Effect in Electron-doped Pr2-xCexCuO4: Superconducting Fluctuations and Two-band Transport
We report a systematic study of normal state Nernst effect in the
electron-doped cuprates PrCeCuO over a wide range of
doping (0.050.21) and temperature. At low temperatures, we
observed a notable vortex Nernst signal above T in the underdoped films,
but no such normal state vortex Nernst signal is found in the overdoped region.
The superconducting fluctuations in the underdoped region are most likely
incoherent phase fluctuations as found in hole-doped cuprates. At high
temperatures, a large normal state Nernst signal is found at dopings from
slightly underdoped to highly overdoped. Combined with normal state
thermoelectric power, Hall effect and magnetoresistance measurements, the large
Nernst effect is compatible with two-band model. For the highly overdoped
films, the large Nernst effect is anomalous and not explainable with a simple
hole-like Fermi surface seen in photoemission experiments.Comment: 9 pages, 8 figures, accepted in PR
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