1,166 research outputs found
Preparation of atomically clean and flat Si(100) surfaces by low-energy ion sputtering and low-temperature annealing
Si(100) surfaces were prepared by wet-chemical etching followed by 0.3-1.5keV
Ar ion sputtering, either at elevated or room temperature. After a brief anneal
under ultrahigh vacuum conditions, the resulting surfaces were examined by
scanning tunneling microscopy. We find that wet-chemical etching alone cannot
produce a clean and flat Si(100) surface. However, subsequent 300eV Ar ion
sputtering at room temperature followed by a 973K anneal yields atomically
clean and flat Si(100) surfaces suitable for nanoscale device fabrication.Comment: 13 pages, 3 figures, to be published in Applied Surface Scienc
Crossover of angular dependent magnetoresistance with the metal-insulator transition in colossal magnetoresistive manganite films
The role of antiphase boundaries during ion sputtering and solid phase epitaxy of Si(001)
The Si(001) surface morphology during ion sputtering at elevated temperatures
and solid phase epitaxy following ion sputtering at room temperature has been
investigated using scanning tunneling microscopy. Two types of antiphase
boundaries form on Si(001) surfaces during ion sputtering and solid phase
epitaxy. One type of antiphase boundary, the AP2 antiphase boundary,
contributes to the surface roughening. AP2 antiphase boundaries are stable up
to 973K, and ion sputtering and solid phase epitaxy performed at 973K result in
atomically flat Si(001) surfaces.Comment: 16 pages, 4 figures, to be published in Surface Scienc
Vertical transport and electroluminescence in InAs/GaSb/InAs structures: GaSb thickness and hydrostatic pressure studies
We have measured the current-voltage (I-V) of type II InAs/GaSb/InAs double
heterojunctions (DHETs) with 'GaAs like' interface bonding and GaSb thickness
between 0-1200 \AA. A negative differential resistance (NDR) is observed for
all DHETs with GaSb thickness 60 \AA below which a dramatic change in the
shape of the I-V and a marked hysteresis is observed. The temperature
dependence of the I-V is found to be very strong below this critical GaSb
thickness. The I-V characteristics of selected DHETs are also presented under
hydrostatic pressures up to 11 kbar. Finally, a mid infra-red
electroluminescence is observed at 1 bar with a threshold at the NDR valley
bias. The band profile calculations presented in the analysis are markedly
different to those given in the literature, and arise due to the positive
charge that it is argued will build up in the GaSb layer under bias. We
conclude that the dominant conduction mechanism in DHETs is most likely to
arise out of an inelastic electron-heavy-hole interaction similar to that
observed in single heterojunctions (SHETs) with 'GaAs like' interface bonding,
and not out of resonant electron-light-hole tunnelling as proposed by Yu et al.
A Zener tunnelling mechanism is shown to contribute to the background current
beyond NDR.Comment: 8 pages 12 fig
Direct observation of particle-hole mixing in the superconducting state by angle-resolved photoemission
Particle-hole (p-h) mixing is a fundamental consequence of the existence of a
pair condensate. We present direct experimental evidence for p-h mixing in the
angle-resolved photoemission (ARPES) spectra in the superconducting state of
Bi_2Sr_2CaCu_2O_{8+\delta}. In addition to its pedagogical importance, this
establishes unambiguously that the gap observed in ARPES is associated with
superconductivity.Comment: 3 pages, revtex, 4 postscript figure
Sliding Luttinger liquid phases
We study systems of coupled spin-gapped and gapless Luttinger liquids. First,
we establish the existence of a sliding Luttinger liquid phase for a system of
weakly coupled parallel quantum wires, with and without disorder. It is shown
that the coupling can {\it stabilize} a Luttinger liquid phase in the presence
of disorder. We then extend our analysis to a system of crossed Luttinger
liquids and establish the stability of a non-Fermi liquid state: the crossed
sliding Luttinger liquid phase (CSLL). In this phase the system exhibits a
finite-temperature, long-wavelength, isotropic electric conductivity that
diverges as a power law in temperature as . This two-dimensional
system has many properties of a true isotropic Luttinger liquid, though at zero
temperature it becomes anisotropic. An extension of this model to a
three-dimensional stack exhibits a much higher in-plane conductivity than the
conductivity in a perpendicular direction.Comment: Revtex, 18 pages, 8 figure
Coupling between planes and chains in YBa2Cu3O7 : a possible solution for the order parameter controversy
We propose to explain the contradictory experimental evidence about the
symmetry of the order parameter in by taking into account
the coupling between planes and chains. This leads to an anticrossing of the
plane and chain band. We include an attractive pairing interaction within the
planes and a repulsive one between planes and chains, leading to opposite signs
for the order parameter on planes and chains, and to nodes of the gap because
of the anticrossing. Our model blends s-wave and d-wave features, and provides
a natural explanation for all the contradictory experimentsComment: 13 pages, revtex, 2 uucoded figure
Core-Collapse Supernovae at the Threshold
Recent progress in modeling core-collapse supernovae is summarized and set in
perspective. Two-dimensional simulations with state-of-the-art treatment of
neutrino transport still fail to produce powerful explosions, but evidence is
presented that they are very close to success.Comment: 8 pages, 3 figures, high-quality available upon request; contribution
to Procs. IAU Coll. 192, "Supernovae", Eds. J.M. Marcaide ad K.W. Weiler,
Springe
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