3,527 research outputs found
Large non-adiabatic hole polarons and matrix element effects in the angle-resolved photoemission spectroscopy of dielectric cuprates
It has been made an extention of the conventional theory based on the
assumption of the well isolated Zhang-Rice singlet to be a first
electron-removal state in dielectric copper oxide. One assumes the photohole
has been localised on either small (pseudo)Jahn-Teller polaron or large
non-adiabatic polaron enclosed one or four to five centers,
respectively, with active one-center valent
manifold. In the framework of the cluster model we have performed a model
microscopic calculation of the -dependence of the matrix element
effects and photon polarization effects for the angle-resolved photoemission in
dielectric cuprate like . We show that effects like the
''remnant Fermi surface'' detected in ARPES experiment for
may be, in fact, a reflection of the matrix element
effects, not a reflection of the original band-structure Fermi surface, or the
strong antiferromagnetic correlations. The measured dispersion-like features in
the low-energy part of the ARPES spectra may be a manifestation of the complex
momentum-dependent spectral line-shape of the large PJT polaron response, not
the dispersion of the well-isolated Zhang-Rice singlet in antiferromagnetic
matrix.Comment: 16 pages, TeX, 9 eps figures adde
Suppression of antiferromagnetic correlations by quenched dipole--type impurities
The effect of quenched random ferromagnetic bonds on the antiferromagnetic
correlation length of a two--dimensional Heisneberg model is studied, applying
the renormalization group method to the classical non--linear sigma model with
quenched random dipole moments. It is found that the antiferromagnetic long
range order is destroyed for any non--zero concentration, of the dipolar
defects, even at zero temperature. Below a line T ~ concentration, the
correlation length is independent of T, and decreases exponentially with
concentration. At higher temperatures, itdecays exponentially with an effective
stiffness constant which decreases with concentration/T. The results are used
to estimate the three--dimensional N\'{e}el temperature, which decays linearly
with at small concentrations, and drops precipitously at a critical
concentration. These predictions are compared with experiments on doped copper
oxides, and are shown to reproduce successfully some of the prominent features
of the data.Comment: 34 pages, LateX, 4 figures Rport-no: TAU
Parametric Generation of Second Sound by First Sound in Superfluid Helium
We report the first experimental observation of parametric generation of
second sound (SS) by first sound (FS) in superfluid helium in a narrow
temperature range in the vicinity of . The temperature dependence
of the threshold FS amplitude is found to be in a good quantitative agreement
with the theory suggested long time ago and corrected for a finite geometry.
Strong amplitude fluctuations and two types of the SS spectra are observed
above the bifurcation. The latter effect is quantitatively explained by the
discreteness of the wave vector space and the strong temperature dependence of
the SS dissipation length.Comment: 4 pages, 4 postscript figures, REVTE
Structural features of highly stable reproducible C₆₀ fullerene aqueous colloid solution probed by various techniques
The method of preparation of highly stable reproducible C₆₀ fullerene aqueous colloid solution is described. The structural organization of C₆₀ fullerenes in aqueous solution was studied and analyzed in detail using various techniques such as chemical analysis, UV/VIS spectroscopy, atomic force and scanning tunneling microscopy, dynamic light scattering, and zeta potential method
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