3,683 research outputs found
Magnons in Ferromagnetic Metallic Manganites
Ferromagnetic (FM) manganites, a group of likely half-metallic oxides, are of
special interest not only because they are a testing ground of the classical
doubleexchange interaction mechanism for the colossal magnetoresistance, but
also because they exhibit an extraordinary arena of emergent phenomena. These
emergent phenomena are related to the complexity associated with strong
interplay between charge, spin, orbital, and lattice. In this review, we focus
on the use of inelastic neutron scattering to study the spin dynamics, mainly
the magnon excitations in this class of FM metallic materials. In particular,
we discussed the unusual magnon softening and damping near the Brillouin zone
boundary in relatively narrow band compounds with strong Jahn-Teller lattice
distortion and charge/orbital correlations. The anomalous behaviors of magnons
in these compounds indicate the likelihood of cooperative excitations involving
spin, lattice, as well as orbital degrees of freedom.Comment: published in J. Phys.: Cond. Matt. 20 figure
Electron-phonon interaction at the Be(0001) surface
We present a first principle study of the electron-phonon (e-p) interaction
at the Be(0001) surface. The real and imaginary part of the e-p self energy are
calculated for the surface state in the binding energy range from the
point to the Fermi level. Our calculation shows an overall good
agreement with several photoemission data measured at high and low
temperatures. Additionally, we show that the energy derivative of real part of
the self-energy presents a strong temperature and energy variation close to
, making it difficult to measure its value just at .Comment: Accepted in Phys. Rev. Lett., 5 figure
Noncontacting device to indicate deflection of turbopump internal rotating parts
Phase 2 (development) which was concluded for the ultrasonic Doppler device and the light-pipe-reflectance device is reported. An ultrasonic Doppler breadboard system was assembled which accurately measured runout in the J-2 LOX pump impeller during operation. The transducer was mounted on the outside of the pump volute using a C-clamp. Vibration was measured by conducting the ultrasonic wave through the volute housing and through the fluid in the volute to the impeller surface. The impeller vibration was also measured accurately using the light-pipe probe mounted in an elastomeric-gland fitting in the pump case. A special epoxy resin developed for cryogenic applications was forced into the end of the fiber-optic probe to retain the fibers. Subsequently, the probe suffered no damage after simultaneous exposure to 2150 psi and 77 F. Preliminary flash X-radiographs were taken of the turbine wheel and the shaft-bearing-seal assembly, using a 2-megavolt X-ray unit. Reasonable resolution and contrast was obtained. A fast-neutron detector was fabricated and sensitivity was measured. The results demonstrated that the technique is feasible for integrated-time measurements requiring, perhaps, 240 revolutions to obtain sufficient exposure at 35,000 rpm. The experimental verification plans are included
Noncontacting devices to indicate deflection and vibration of turbopump internal rotating parts
Published report discusses feasibility of ultrasonic techniques; neutron techniques; X-radiography; optical devices; gamma ray devices; and conventional displacement sensors. Use of signal transmitters in place of slip rings indicated possible improvement and will be subject of futher study
A Field Effect Transitor based on the Mott Transition in a Molecular Layer
Here we propose and analyze the behavior of a FET--like switching device, the
Mott transition field effect transistor, operating on a novel principle, the
Mott metal--insulator transition. The device has FET-like characteristics with
a low ``ON'' impedance and high ``OFF'' impedance. Function of the device is
feasible down to nanoscale dimensions. Implementation with a class of organic
charge transfer complexes is proposed.Comment: Revtex 11pages, Figures available upon reques
Evidence for Strong Itinerant Spin Fluctuations in the Normal State of CeFeAsO(0.89)F(0.11) Iron-Oxypnictides
The electronic structure in the normal state of CeFeAsO0.89F0.11 oxypnictide
superconductors has been investigated with x-ray absorption and photoemission
spectroscopy. All the data exhibit signatures of Fe d-electron itinerancy.
Exchange multiplets appearing in the Fe 3s core level indicate the presence of
itinerant spin fluctuations. These findings suggest that the underlying physics
and the origin of superconductivity in these materials are likely to be quite
different from those of the cuprate high-temperature superconductors. These
materials provide opportunities for elucidating the role of magnetic
fluctuations in high-temperature superconductivity.Comment: Shorter version. Accepted in Phys. Rev. Let
Fermions and bosons in nonsymmorphic PdSb2 with sixfold degeneracy
PdSb2 is a candidate for hosting 6-fold-degenerate exotic fermions (beyond
Dirac and Weyl fermions).The nontrivial band crossing protected by the
nonsymmorphic symmetry plays a crucial role in physical properties. We have
grown high-quality single crystals of PdSb2 and characterized their physical
properties under several stimuli (temperature, magnetic field, and pressure).
While it is a diamagnetic Fermi-liquid metal under ambient pressure, PdSb2
exhibits a large magnetoresistance with continuous increase up to 14 T, which
follows the Kohler's scaling law at all temperatures. This implies one-band
electrical transport, although multiple bands are predicted by first principles
calculations. By applying magnetic field along the [111] direction, de Haas-van
Alphen oscillations are observed with frequency of 102 T. The effective mass is
nearly zero (0.045m0) with the Berry phase close to {\pi}, confirming that the
band close to the R point has a nontrivial character. Under quasihydrostatic
pressure (p), evidence for superconductivity is observed in the resistivity
below the critical temperature Tc. The dome-shaped Tc versus p is obtained with
maximum Tc~2.9 K. We argue that the formation of Cooper pairs (bosons) is the
consequence of the redistribution of the 6-fold-degenerate fermions under
pressure
- …