974 research outputs found
The spontaneous emergence of ordered phases in crumpled sheets
X-ray tomography is performed to acquire 3D images of crumpled aluminum
foils. We develop an algorithm to trace out the labyrinthian paths in the three
perpendicular cross sections of the data matrices. The tangent-tangent
correlation function along each path is found to decay exponentially with an
effective persistence length that shortens as the crumpled ball becomes more
compact. In the mean time, we observed ordered domains near the crust, similar
to the lamellae phase mixed by the amorphous portion in lyotropic liquid
crystals. The size and density of these domains grow with further compaction,
and their orientation favors either perpendicular or parallel to the radial
direction. Ordering is also identified near the core with an arbitrary
orientation, exemplary of the spontaneous symmetry breaking
Single shot phase contrast imaging using laser-produced Betatron x-ray beams
Development of x-ray phase contrast imaging applications with a laboratory
scale source have been limited by the long exposure time needed to obtain one
image. We demonstrate, using the Betatron x-ray radiation produced when
electrons are accelerated and wiggled in the laser-wakefield cavity, that a
high quality phase contrast image of a complex object (here, a bee), located in
air, can be obtained with a single laser shot. The Betatron x-ray source used
in this proof of principle experiment has a source diameter of 1.7 microns and
produces a synchrotron spectrum with critical energy E_c=12.3 +- 2.5 keV and
10^9 photons per shot in the whole spectrum.Comment: 3 pages, 3 figure
Interpretation of Photoemission Spectra of (TaSe4)2I as Evidence of Charge Density Wave Fluctuations
The competition between different and unusual effects in
quasi-one-dimensional conductors makes the direct interpretation of
experimental measurements of these materials both difficult and interesting. We
consider evidence for the existence of large charge-density-wave fluctuations
in the conducting phase of the Peierls insulator (TaSe4)2I, by comparing the
predictions of a simple Lee, Rice and Anderson theory for such a system with
recent angle-resolved photoemission spectra. The agreement obtained suggests
that many of the unusual features of these spectra may be explained in this
way. This view of the system is contrasted with the behaviour expected of a
Luttinger liquid.Comment: Archive copy of published paper. 19 pages, 12 figures, uses IOP
macro
S and D Wave Mixing in High Superconductors
For a tight binding model with nearest neighbour attraction and a small
orthorhombic distortion, we find a phase diagram for the gap at zero
temperature which includes three distinct regions as a function of filling. In
the first, the gap is a mixture of mainly -wave with a smaller extended
-wave part. This is followed by a region in which there is a rapid increase
in the -wave part accompanied by a rapid increase in relative phase between
and from 0 to . Finally, there is a region of dominant with a
mixture of and zero phase. In the mixed region with a finite phase, the
-wave part of the gap can show a sudden increase with decreasing temperature
accompanied with a rapid increase in phase which shows many of the
characteristics measured in the angular resolved photoemission experiments of
Ma {\em et al.} in Comment: 12 pages, RevTeX 3.0, 3 PostScript figures uuencoded and compresse
Profile-Guided Automatic Inline Expansion for C Programs
Coordinated Science Laboratory was formerly known as Control Systems LaboratoryNational Science Foundation / MIP-8809478NCRAMD 29K Advanced Processor Development DivisionNational Aeronautics and Space Administration / NASA NAG 1-61
Boundary Effects on Spectral Properties of Interacting Electrons in One Dimension
The single electron Green's function of the one-dimensional
Tomonaga-Luttinger model in the presence of open boundaries is calculated with
bosonization methods. We show that the critical exponents of the local spectral
density and of the momentum distribution change in the presence of a boundary.
The well understood universal bulk behavior always crosses over to a boundary
dominated regime for small energies or small momenta. We show this crossover
explicitly for the large-U Hubbard model in the low-temperature limit.
Consequences for photoemission experiments are discussed.Comment: revised and reformatted paper to appear in Phys. Rev. Lett. (Feb.
1996). 5 pages (revtex) and 3 embedded figures (macro included). A complete
postscript file is available from http://FY.CHALMERS.SE/~eggert/luttinger.ps
or by request from [email protected]
Critical Properties of Spectral Functions for the 1D Anisotropic t-J Models with an Energy Gap
We exactly calculate the momentum-dependent critical exponents for spectral
functions in the one-dimensional anisotropic t-J models with a gap either in
the spin or charge excitation spectrum. Our approach is based on the Bethe
ansatz technique combined with finite-size scaling techniques in conformal
field theory. It is found that the spectral functions show a power-law
singularity, which occurs at frequencies determined by the dispersion of a
massive spin (or charge) excitation.We discuss how the nontrivial contribution
of a massive excitation controls the singular behavior in optical response
functions.Comment: 4 pages, REVTeX, 2 figures(available upon request), accepted for
publication in JPSJ 66 (1997) No.
- …