330 research outputs found
Aluminophosphate molecular sieves comprised of hydrated triple crankshaft chains
We report the first synthesis of pure aluminophosphate hydrate H2 (AlPO4-H2) and its structure; AlPO4-H2 is constructed exclusively from a hydrated chain building unit that also builds the 18-ring VPI-5 structure and has one-dimensional channels circumscribed by highly elliptical rings consisting often oxygen atoms, implications from the existence of this building unit for the synthesis of novel aluminophosphate molecular sieves and for the synthesis of aluminosilicate and silicate analogues of AlPO4-H2 and VPI-5 are discussed
Electronic structure of PrCaMnO near the Fermi level studied by ultraviolet photoelectron and x-ray absorption spectroscopy
We have investigated the temperature-dependent changes in the near-
occupied and unoccupied states of PrCaMnO which shows the
presence of ferromagnetic and antiferromagnetic phases. The
temperature-dependent changes in the charge and orbital degrees of freedom and
associated changes in the Mn 3 - O 2 hybridization result in varied O
2 contributions to the valence band. A quantitative estimate of the charge
transfer energy () shows a larger value compared to the earlier
reported estimates. The charge localization causing the large is
discussed in terms of different models including the electronic phase
separation.Comment: 19 pages, 7 figures, To be published in Phy. Rev.
Space Charge Effect and Mirror Charge Effect in Photoemission Spectroscopy
We report the observation and systematic investigation of the space charge
effect and mirror charge effect in photoemission spectroscopy. When pulsed
light is incident on a sample, the photoemitted electrons experience energy
redistribution after escaping from the surface because of the Coulomb
interaction between them (space charge effect) and between photoemitted
electrons and the distribution of mirror charges in the sample (mirror charge
effect). These combined Coulomb interaction effects give rise to an energy
shift and a broadening which can be on the order of 10 meV for a typical
third-generation synchrotron light source. This value is comparable to many
fundamental physical parameters actively studied by photoemission spectroscopy
and should be taken seriously in interpreting photoemission data and in
designing next generation experiments.Comment: Journal of Electron Spectroscopy and Related Phenomena 142(2004)27-3
Two-hole bound states in modified t-J model
We consider modified model with minimum of single-hole dispersion at
the points , . It is shown that two holes on
antiferromagnetic background produce a bound state which properties strongly
differs from the states known in the unmodified model. The bound state is
d-wave, it has four nodes on the face of the magnetic Brillouin zone. However,
in the coordinate representation it looks like as usual s-wave.Comment: LaTeX 9 page
Properties of electrons near a Van Hove singularity
The Fermi surface of most hole-doped cuprates is close to a Van Hove
singularity at the M point. A two-dimensional electronic system, whose Fermi
surface is close to a Van Hove singularity shows a variety of weak coupling
instabilities. It is a convenient model to study the interplay between
antiferromagnetism and anisotropic superconductivity. The renormalization group
approach is reviewed with emphasis on the underlying physical processes.
General properties of the phase diagram and possible deformations of the Fermi
surface due to the Van Hove proximity are described.Comment: Proceedings of SNS-01 to appear in the Journal of Physics and
Chemistry of Solids, SNS-0
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