6,053 research outputs found
Ce doping in T-La2CuO4 films: Broken electron-hole symmetry for high-Tc superconductivity
We attempted Ce doping in La2CuO4 with the K2NiF4 (T) structure by molecular
beam epitaxy. At low growth temperature and with an appropriate substrate
choice, we found that Ce can be incorporated into the K2NiF4 lattice up to x ~
0.06, which had not yet been realized in bulk synthesis. The doping of Ce makes
T-La2-xCexCuO4 more insulating, which is in sharp contrast to Ce doping in
La2CuO4 with the Nd2CuO4 structure, which makes the compounds superconducting.
The observed smooth increase in resistivity from hole-doped side
(T-La2-xSrxCuO4) to electron-doped side (T-La2-xCexCuO4) indicates that
electron-hole symmetry is broken in the T-phase materials.Comment: proceedings of ISS 200
Nucleotide Sequence of a cDNA for 1-Aminocyclopropane-1-Carboxylate Synthase from Melon Fruits
Cosmological Baryon Sound Waves Coupled with the Primeval Radiation
The fluid equations for the baryon-electron system in an expanding universe
are derived from the Boltzmann equation. The effect of the Compton interaction
is taken into account properly in order to evaluate the photon-electron
collisional term. As an application, the acoustic motions of the
baryon-electron system after recombination are investigated. The effective
adiabatic index is computed for sound waves of various wavelengths,
assuming the perturbation amplitude is small. The oscillations are found to be
dumped when changes from between 1 (for an isothermal process) to 5/3
(for an adiabatic process).Comment: 20 pages, Revtex, Accepted for publication in Phys. Rev.
Equation of motion for a domain wall coupled to gravitational field
The equation of motion for a domain wall coupled to gravitational field is
derived from the Nambu-Goto action. The domain wall is treated as a source of
gravitational field. The perturbed equation is also obtained with gravitational
back reaction on the wall motion taken into account. For general spherically
symmetric background case, the equation is expressed in terms of the
gauge-invariant variables.Comment: 13 pages, latex, no figures, uses REVTe
Effects of abscisic acid treatment and night temperatures on anthocyanin composition in Pinot noir grapes
Potted Pinot noir grapevines were grown under continuous high temperature (30 °C) or low night (15 °C) and high day (30 °C) temperatures after veraison. Half of the total number of clusters of each vine was sprayed with 250 ppm abscisic acid (ABA) at veraison. Anthocyanin accumulation in berry skins grown under high night temperatures was lower than that in berries grown under low night temperatures. HPLC analysis showed that the ratios of delphinidin-3-glucoside, cyanidin-3-glucoside and petunidin-3-glucoside to the total anthocyanin content were greatly reduced under high night temperatures. ABA treatment enhanced anthocyanin accumulation under high night temperatures to almost the same level as under low night temperatures; the ratio of each anthocyanin to the total anthocyanin, however, was not affected by ABA treatment.
New class of T-prime-structure cuprate superconductors
High-temperature superconductivity has been discovered in La2-xBaxCuO4 [1], a
compound that derives from the undoped La2CuO4 crystallizing in the perovskite
T-structure. In this structure oxygen octahedra surround the copper ions. It is
common knowledge that charge carriers induced by doping in such an undoped
antiferromagnetic Mott-insulator lead to high-temperature superconductivity [2-
4]. The undoped material La2CuO4 is also the basis of the electron-doped
cuprate superconductors [5] of the form La2-xCexCuO4+y [6,7] which however
crystallize in the so called T-prime-structure, i.e. without apical oxygen
above or below the copper ions of the CuO2-plane. It is well known that for
La2-xCexCuO4+y the undoped T-prime-structure parent compound cannot be prepared
due to the structural phase transition back into the T-structure occuring
around x ~ 0.05. Here, we report that if La is substituted by RE = Y, Lu, Sm,
Eu, Gd, or Tb, which have smaller ionic radii but have the same valence as La,
nominally undoped La2-xRExCuO4 can be synthesized by molecular beam epitaxy in
the T-prime-structure. The second important result is that all these new
T-prime-compounds are superconductors with fairly high critical temperatures up
to 21 K. For this new class of cuprates La2-xRExCuO4, which forms the
T-prime-parent compounds of the La-based electron doped cuprates, we have not
been able to obtain the Mott-insulating ground state for small x before the
structural phase transition into the T-structure takes place.Comment: 17 pages, 7 figure
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