13,538 research outputs found
Scintillation observations at medium latitude geomagnetically conjugate stations
Scintillation observations at medium latitude geomagnetically conjugate station
Quasi-Homogeneous Backward-Wave Plasmonic Structures: Theory and Accurate Simulation
Backward waves and negative refraction are shown to exist in plasmonic
crystals whose lattice cell size is a very small fraction of the vacuum
wavelength (less than 1/40th in an illustrative example). Such
``quasi-homogeneity'' is important, in particular, for high-resolution imaging.
Real and complex Bloch bands are computed using the recently developed
finite-difference calculus of ``Flexible Local Approximation MEthods'' (FLAME)
that produces linear eigenproblems, as opposed to quadratic or nonlinear ones
typical for other techniques. FLAME dramatically improves the accuracy by
incorporating local analytical approximations of the solution into the
numerical scheme.Comment: 4 pages, 3 figure
Quasiparticle spectroscopy and high-field phase diagrams of cuprate superconductors -- An investigation of competing orders and quantum criticality
We present scanning tunneling spectroscopic and high-field thermodynamic
studies of hole- and electron-doped (p- and n-type) cuprate superconductors.
Our experimental results are consistent with the notion that the ground state
of cuprates is in proximity to a quantum critical point (QCP) that separates a
pure superconducting (SC) phase from a phase comprised of coexisting SC and a
competing order, and the competing order is likely a spin-density wave (SDW).
The effect of applied magnetic field, tunneling current, and disorder on the
revelation of competing orders and on the low-energy excitations of the
cuprates is discussed.Comment: 10 pages, 5 figures. Accepted for publication in the International
Journal of Modern Physics B. (Correspondence author: Nai-Chang Yeh, e-mail:
[email protected]
Evolution of superconductivity by oxygen annealing in FeTe0.8S0.2
Oxygen annealing dramatically improved the superconducting properties of
solid-state-reacted FeTe0.8S0.2, which showed only a broad onset of
superconducting transition just after the synthesis. The zero resistivity
appeared and reached 8.5 K by the oxygen annealing at 200\degree C. The
superconducting volume fraction was also enhanced from 0 to almost 100%. The
lattice constants were compressed by the oxygen annealing, indicating that the
evolution of bulk superconductivity in FeTe0.8S0.2 was correlated to the
shrinkage of lattice.Comment: 13 pages, 6 figure
Radiation pattern of a classical dipole in a photonic crystal: photon focusing
The asymptotic analysis of the radiation pattern of a classical dipole in a
photonic crystal possessing an incomplete photonic bandgap is presented. The
far-field radiation pattern demonstrates a strong modification with respect to
the dipole radiation pattern in vacuum. Radiated power is suppressed in the
direction of the spatial stopband and strongly enhanced in the direction of the
group velocity, which is stationary with respect to a small variation of the
wave vector. An effect of radiated power enhancement is explained in terms of
\emph{photon focusing}. Numerical example is given for a square-lattice
two-dimensional photonic crystal. Predictions of asymptotic analysis are
substantiated with finite-difference time-domain calculations, revealing a
reasonable agreement.Comment: Submitted to Phys. Rev.
Dimensionality of superconductivity in the infinite-layer high-temperature cuprate Sr0.9M0.1CuO2 (M = La, Gd)
The high magnetic field phase diagram of the electron-doped infinite layer
high-temperature superconducting (high-T_c) compound Sr_{0.9}La_{0.1}CuO_2 was
probed by means of penetration depth and magnetization measurements in pulsed
fields to 60 T. An anisotropy ratio of 8 was detected for the upper critical
fields with H parallel (H_{c2}^{ab}) and perpendicular (H_{c2}^c) to the CuO_2
planes, with H_{c2}^{ab} extrapolating to near the Pauli paramagnetic limit of
160 T. The longer superconducting coherence length than the lattice constant
along the c-axis indicates that the orbital degrees of freedom of the pairing
wavefunction are three dimensional. By contrast, low-field magnetization and
specific heat measurements of Sr_{0.9}Gd_{0.1}CuO_2 indicate a coexistence of
bulk s-wave superconductivity with large moment Gd paramagnetism close to the
CuO_2 planes, suggesting a strong confinement of the spin degrees of freedom of
the Cooper pair to the CuO_2 planes. The region between H_{c2}^{ab} and the
irreversibility line in the magnetization, H_{irr}^{ab}, is anomalously large
for an electron-doped high-T_c cuprate, suggesting the existence of additional
quantum fluctuations perhaps due to a competing spin-density wave order.Comment: 4 pages, 4 figures, submitted to Phys. Rev. B, Rapid Communications
(2004). Corresponding author: Nai-Chang Yeh (E-mail: [email protected]
Properties of entangled photon pairs generated in one-dimensional nonlinear photonic-band-gap structures
We have developed a rigorous quantum model of spontaneous parametric
down-conversion in a nonlinear 1D photonic-band-gap structure based upon
expansion of the field into monochromatic plane waves. The model provides a
two-photon amplitude of a created photon pair. The spectra of the signal and
idler fields, their intensity profiles in the time domain, as well as the
coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are
determined both for cw and pulsed pumping regimes in terms of the two-photon
amplitude. A broad range of parameters characterizing the emitted
down-converted fields can be used. As an example, a structure composed of 49
layers of GaN/AlN is analyzed as a suitable source of photon pairs having high
efficiency.Comment: 14 pages, 23 figure
Experimental investigation of the competing orders and quantum criticality in hole- and electron-doped cuprate superconductors
We investigate the issues of competing orders and quantum criticality in cuprate superconductors via experimental studies of the high-field thermodynamic phase diagrams and the quasiparticle tunneling spectroscopy. Substantial field-induced quantum fluctuations are found in all cuprates investigated, and the corresponding correlation with quasiparticle spectra suggest that both electron- (n-type) and hole-doped (p-type) cuprate superconductors are in close proximity to a quantum critical point that separates a pure superconducting (SC) phase from a phase consisting of coexisting SC and a competing order. We further suggests that the relevant competing order is likely a spin-density wave (SDW) or a charge density wave (CDW), which can couple efficiently to an in-plane Cu-O bond stretching longitudinal optical (LO) phonon mode in the p-type cuprates but not in the n-type cuprates. This cooperative interaction may account for the pseudogap phenomenon above T, only in the p-type cuprate superconductors
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