38,248 research outputs found
Drift waves in the linear regime
Verifying drift wave linear theory by external excitation of drift waves in collision plasm
Superconductivity in spinel oxide LiTi2O4 epitaxial thin films
LiTi2O4 is a unique material in that it is the only known oxide spinel
superconductor. Although bulk studies have demonstrated that superconductivity
can be generally described by the Bardeen-Cooper-Schreiffer theory, the
microscopic mechanisms of superconductivity are not yet resolved fully. The
sensitivity of the superconducting properties to various defects of the spinel
crystal structure provides insight into such mechanisms. Epitaxial films of
LiTi2O4 on single crystalline substrates of MgAl2O4, MgO, and SrTiO3 provide
model systems to systematically explore the effects of lattice strain and
microstructural disorder. Lattice strain that affects bandwidth gives rise to
limited variations in the superconducting and normal state properties.
Microstructural disorder such as antiphase boundaries that give rise to Ti
network disorder can reduce the critical temperature, but Ti network disorder
combined with Mg interdiffusion can affect the superconducting state much more
dramatically. Thickness dependent transport studies indicate a
superconductor-insulator transition as a function of film thickness regardless
of lattice strain and microstructure. In addition, surface sensitive X-ray
absorption spectroscopy has identified Ti to retain site symmetry and average
valence of the bulk material regardless of film thickness.Comment: 25 pages, 7 figures, v2 - expanded Fig 1,2,7 with added discussion
Anomalous Soft Photons in Hadron Production
Anomalous soft photons in excess of what is expected from electromagnetic
bremsstrahlung have been observed in association with the production of
hadrons, mostly mesons, in high-energy (K+)p, (pi+)p, (pi-)p, pp, and (e+)(e-)
collisions. We propose a model for the simultaneous production of anomalous
soft photons and mesons in quantum field theory, in which the meson production
arises from the oscillation of color charge densities of the quarks of the
underlying vacuum in the flux tube. As a quark carries both a color charge and
an electric charge, the oscillation of the color charge densities will be
accompanied by the oscillation of electric charge densities, which will in turn
lead to the simultaneous production of soft photons during the meson production
process. How the production of these soft photons may explain the anomalous
soft photon data will be discussed. Further experimental measurements to test
the model will be proposed.Comment: 19 pages, 2 figures, to be published in Physical Review
Spin-transfer mechanism for magnon-drag thermopower
We point out a relation between the dissipative spin-transfer-torque
parameter and the contribution of magnon drag to the thermoelectric
power in conducting ferromagnets. Using this result we estimate in iron
at low temperatures, where magnon drag is believed to be the dominant
contribution to the thermopower. Our results may be used to determine
from magnon-drag-thermopower experiments, or, conversely, to infer the strength
of magnon drag via experiments on spin transfer
Novel Bose-Einstein Interference in the Passage of a Fast Particle in a Dense Medium
When an energetic particle collides coherently with many medium particles at
high energies, the Bose-Einstein symmetry with respect to the interchange of
the exchanged virtual bosons leads to a destructive interference of the Feynman
amplitudes in most regions of the phase space but a constructive interference
in some other regions of the phase space. As a consequence, the recoiling
medium particles have a tendency to come out collectively along the direction
of the incident fast particle, each carrying a substantial fraction of the
incident longitudinal momentum. Such an interference appearing as collective
recoils of scatterers along the incident particle direction may have been
observed in angular correlations of hadrons associated with a high-
trigger in high-energy AuAu collisions at RHIC.Comment: 10 pages, 2 figures, invited talk presented at the 35th Symposium on
Nuclear Physics, Cocoyoc, Mexico, January 3, 2012, to be published in IOP
Conference Serie
The role of magnetic anisotropy in spin filter junctions
We have fabricated oxide based spin filter junctions in which we demonstrate
that magnetic anisotropy can be used to tune the transport behavior of spin
filter junctions. Until recently, spin filters have been largely comprised of
polycrystalline materials where the spin filter barrier layer and one of the
electrodes are ferromagnetic. These spin filter junctions have relied on the
weak magnetic coupling between one ferromagnetic electrode and a barrier layer
or the insertion of a nonmagnetic insulating layer in between the spin filter
barrier and electrode. We have demonstrated spin filtering behavior in
La0.7Sr0.3MnO3/chromite/Fe3O4 junctions without nonmagnetic spacer layers where
the interface anisotropy plays a significant role in determining transport
behavior. Detailed studies of chemical and magnetic structure at the interfaces
indicate that abrupt changes in magnetic anisotropy across the
non-isostructural interface is the cause of the significant suppression of
junction magnetoresistance in junctions with MnCr2O4 barrier layers.Comment: 7 pages, 7 figure
Azimuthal Asymmetry of Direct Photons in High Energy Nuclear Collisions
We show that a sizeable azimuthal asymmetry, characterized by a coefficient
v_2, is to be expected for direct photons produced in non-central high energy
nuclear collisions. This signal is generated by photons radiated by jets
interacting with the surrounding hot plasma. The anisotropy is out of phase by
an angle with respect to that associated with the elliptic anisotropy
of hadrons, leading to negative values of v_2. Such an asymmetry, if observed,
could be a signature for the presence of a quark gluon plasma and would
establish the importance of jet-plasma interactions as a source of
electromagnetic radiation.Comment: New title. Final versio
Radial Flow from Electromagnetic Probes and Signal of Quark Gluon Plasma
A first attempt has been made to extract the evolution of radial flow from
the analysis of the experimental data on electromagnetic probes experimentally
measured at SPS and RHIC energies. The spectra of photons and dileptons
measured by WA98 and NA60 collaborations respectively at CERN-SPS and the
photon spectra obtained by PHENIX collaboration at BNL-RHIC have been used to
constrain the theoretical models, rendering the outcome of the analysis largely
model independent. We argue that the variation of the radial velocity with
invariant mass is indicative of a phase transition from initially produced
partons to hadrons at SPS and RHIC energies.Comment: One LaTeX and 9 eps files, to appear in Phys. Rev.
- …