4,144 research outputs found
Large anisotropy in the optical conductivity of YNi2B2C
The optical properties of YNiBC are studied by using the
first-principles full-potential linearized augmented plane wave (FLAPW) method
within the local density approximation. Anisotropic behavior is obtained in the
optical conductivity, even though the electronic structure shows 3D character.
A large peak in is obtained at 2.4 eV. The anisotropic optical
properties are analyzed in terms of interband transitions between energy levels
and found that the Ni site plays an important role. The electronic energy loss
spectroscopy (EELS) spectra are also calculated to help elucidate the
anisotropic properties in this system.Comment: revtex4, 4 pages, 5 figures, to appear in PR
Spatial and temporal characterization of a Bessel beam produced using a conical mirror
We experimentally analyze a Bessel beam produced with a conical mirror,
paying particular attention to its superluminal and diffraction-free
properties. We spatially characterized the beam in the radial and on-axis
dimensions, and verified that the central peak does not spread over a
propagation distance of 73 cm. In addition, we measured the superluminal phase
and group velocities of the beam in free space. Both spatial and temporal
measurements show good agreement with the theoretical predictions.Comment: 5 pages, 6 figure
Fermi surface of the colossal magnetoresistance perovskite La_{0.7}Sr_{0.3}MnO_{3}
Materials that exhibit colossal magnetoresistance (CMR) are currently the
focus of an intense research effort, driven by the technological applications
that their sensitivity lends them to. Using the angular correlation of photons
from electron-positron annihilation, we present a first glimpse of the Fermi
surface of a material that exhibits CMR, supported by ``virtual crystal''
electronic structure calculations. The Fermi surface is shown to be
sufficiently cubic in nature that it is likely to support nesting.Comment: 5 pages, 5 PS figure
Observation of First-Order Metal-Insulator Transition without Structural Phase Transition in VO_2
An abrupt first-order metal-insulator transition (MIT) without structural
phase transition is first observed by current-voltage measurements and
micro-Raman scattering experiments, when a DC electric field is applied to a
Mott insulator VO_2 based two-terminal device. An abrupt current jump is
measured at a critical electric field. The Raman-shift frequency and the
bandwidth of the most predominant Raman-active A_g mode, excited by the
electric field, do not change through the abrupt MIT, while, they, excited by
temperature, pronouncedly soften and damp (structural MIT), respectively. This
structural MIT is found to occur secondarily.Comment: 4 pages, 4 figure
Spitzer Parallax of OGLE-2018-BLG-0596: A Low-mass-ratio Planet around an M Dwarf
We report the discovery of a Spitzer microlensing planet OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio q ~ 2 × 10^(−4). The planetary signal, which is characterized by a short (~1 day) "bump" on the rising side of the lensing light curve, was densely covered by ground-based surveys. We find that the signal can be explained by a bright source that fully envelops the planetary caustic, i.e., a "Hollywood" geometry. Combined with the source proper motion measured from Gaia, the Spitzer satellite parallax measurement makes it possible to precisely constrain the lens physical parameters. The preferred solution, in which the planet perturbs the minor image due to lensing by the host, yields a Uranus-mass planet with a mass of M_p = 13.9 ± 1.6 M⊕ orbiting a mid M-dwarf with a mass of M_h = 0.23 ± 0.03 M⊙. There is also a second possible solution that is substantially disfavored but cannot be ruled out, for which the planet perturbs the major image. The latter solution yields M_p = 1.2 ± 0.2 M⊕ and M_h = 0.15 ± 0.02 M⊙. By combining the microlensing and Gaia data together with a Galactic model, we find in either case that the lens lies on the near side of the Galactic bulge at a distance D_L ~ 6 ± 1 kpc. Future adaptive optics observations may decisively resolve the major image/minor image degeneracy
- …