4,703 research outputs found
Mineral composition of ores and silicagel quality
Mineral composition and silica hydrogel properties of Japanese acid clay or
Classical Solutions of Ghost Condensation Models
Motivated by ideas obtained from both ghost condensation and gravitational
Higgs mechanism, we attempt to find classical solutions in the unitary gauge in
general ghost condensation models. It is shown that depending on the form of
scalar fields in an action, there are three kinds of exact solutions, which are
(anti-) de Sitter space-time, polynomially expanding universes and flat
Minkowski space-time. We briefly comment on gravitational Higgs mechanism in
these models where we have massive gravitons of 5 degrees of freedom and 1
unitary scalar field (Nambu-Goldstone boson) after spontaneous symmetry
breakdown of general coordinate reparametrization invariance. The models at
hand are free from the problem associated with the non-unitary propagating
mode.Comment: 9 pages, no figure
Prediction of Orbital Ordering in Single-Layered Ruthenates
The key role of the orbital degree of freedom to understand the magnetic
properties of layered ruthenates is here discussed. In the G-type
antiferromagnetic phase of CaRuO, recent X-ray experiments reported the
presence of 0.5 hole per site in the orbital, while the
and orbitals contain 1.5 holes. This unexpected hole
distribution is explained by a novel state with orbital ordering (OO),
stabilized by a combination of Coulomb interactions and lattice distortions. In
addition, the rich phase diagram presented here suggests the possibility of
large magnetoresistance effects, and predicts a new ferromagnetic OO phase in
ruthenates.Comment: 4 pages, Revtex, with 2 figures embedded in the text. Submitted to
Phys. Rev. Let
Quasi-particle Density in Sr2RuO4 Probed by means of the Phonon Thermal Conductivity
The thermal conductivity of Sr2RuO4 along the least conducting direction
perpendicular to the RuO2 plane has been studied down to 0.3 K. In this
configuration the phonons remain the dominant heat carriers down to the lowest
temperature, and their conductivity in the normal state is determined by the
scattering on conduction electrons. We show that the phonon mean free path in
the superconducting state is sensitive to the density of the quasi-particles in
the bulk. An unusual magnetic field dependence of the phonon thermal
conductivity is ascribed to the anisotropic superconducting gap structure in
Sr2RuO4.Comment: 14 pages, 6 eps figures, Latex. This article corresponds to the
reference 25 of Phys. Rev. Lett. vol.86 page2649-2652 (2001) and
cond-mat/010449
Phase transition in the 3 Kelvin phase in the eutectic Sr2RuO4-Ru
The inhomogeneous 3-Kelvin (3K) phase of the eutectic Sr2RuO4 with Ru
inclusions nucleates superconductivity at the interface between Ru and Sr2RuO4.
The structure of the interface state and its physical properties are examined
here. Two superconducting phases are identified between the transitions to the
bulk phase at 1.5K and to the 3K phase. The nucleation of the 3K phase results
in a state conserving time reversal symmetry, which generates an intrinsically
frustrated superconducting network in samples with many Ru inclusions. At a
lower temperature (>1.5K), a discontinuous (first order) transition to an
interface state breaking time reversal symmetry is found leading to an
unfrustrated network phase. It is shown that this phase transition located at a
temperature between 1.5 and 3K would yield the anomalous property that the
critical current in such a network depends on the sign of the current,
reproducing recent experimental observations.Comment: This paper has been withdrawn by the authors. 5 pages, 6 figure
Mechanism of hopping transport in disordered Mott insulators
By using a combination of detailed experimental studies and simple
theoretical arguments, we identify a novel mechanism characterizing the hopping
transport in the Mott insulating phase of CaSrRuO near the
metal-insulator transition. The hopping exponent shows a systematic
evolution from a value of deeper in the insulator to the
conventional Mott value closer to the transition. This behavior,
which we argue to be a universal feature of disordered Mott systems close to
the metal-insulator transition, is shown to reflect the gradual emergence of
disorder-induced localized electronic states populating the Mott-Hubbard gap.Comment: 5 pages, 3 figures, To be published in Physical Review Letter
Upper Critical Field of the 3 Kelvin Phase in Sr2RuO4
The inhomogeneous 3 Kelvin phase is most likely a superconducting state
nucleating at the interface between micrometer-sized Ru-metal inclusions and
Sr2RuO4 above the bulk onset of superconductivity. This filamentary
superconducting state yields a characteristic temperature dependence of the
upper critical field which is sublinear, i.e., H_{c2} (T) \propto (T^* -
T)^{\gamma} with 0.5 \leq \gamma < 1 (T^*: nucleation temperature). The
Ginzburg-Landau theory is used to analyze the behavior of the nucleated
spin-triplet phase in a field and the characteristic features of H_{c2}
observed in the experiment are explained based on a two-component order
parameter in the presence of a filament of enhanced superconductivity with a
finite width.Comment: 4 pages, 3 figure
Unconventional Anomalous Hall Effect in the Metallic Triangular-Lattice Magnet PdCrO2
We experimentally reveal an unconventional anomalous Hall effect (UAHE) in a
quasi-two-dimensional triangular-lattice antiferromagnet PdCrO2. Using high
quality single crystals of PdCrO2, we found that the Hall resistivity deviates
from the conventional behavior below T* = 20 K, noticeably lower than TN = 37.5
K, at which Cr^{3+} (S=3/2) spins order in a 120 degree structure. In view of
the theoretical expectation that the spin chirality cancels out in the simplest
120 degree spin structure, we discuss required conditions for the emergence of
UAHE within Berry-phase mechanisms.Comment: 4 pages, 5 figures, accepted for publication in PR
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