172 research outputs found
Magnetic fluctuations in n-type high- superconductors reveal breakdown of fermiology
By combining experimental measurements of the quasiparticle and dynamical
magnetic properties of optimally electron-doped PrLaCeCuO
with theoretical calculations we demonstrate that the conventional fermiology
approach cannot possibly account for the magnetic fluctuations in these
materials. In particular, we perform tunneling experiments on the very same
sample for which a dynamical magnetic resonance has been reported recently and
use photoemission data by others on a similar sample to characterize the
fermionic quasiparticle excitations in great detail. We subsequently use this
information to calculate the magnetic response within the conventional
fermiology framework as applied in a large body of work for the hole-doped
superconductors to find a profound disagreement between the theoretical
expectations and the measurements: this approach predicts a step-like feature
rather than a sharp resonance peak, it underestimates the intensity of the
resonance by an order of magnitude, it suggests an unreasonable temperature
dependence of the resonance, and most severely, it predicts that most of the
spectral weight resides in incommensurate wings which are a key feature of the
hole-doped cuprates but have never been observed in the electron-doped
counterparts. Our findings strongly suggest that the magnetic fluctuations
reflect the quantum-mechanical competition between antiferromagnetic and
superconducting orders.Comment: 10 pages, 9 figures, 1 tabl
Magnetic quantum oscillations in YBaCuO and YBaCuO in fields of up to 85 T; patching the hole in the roof of the superconducting dome
We measure magnetic quantum oscillations in the underdoped cuprates
YBaCuO with , 0.69, using fields of up to 85 T. The
quantum-oscillation frequencies and effective masses obtained suggest that the
Fermi energy in the cuprates has a maximum at . On either
side, the effective mass may diverge, possibly due to phase transitions
associated with the T=0 limit of the metal-insulator crossover (low- side),
and the postulated topological transition from small to large Fermi surface
close to optimal doping (high side)
Influence of definition based versus pragmatic birth registration on international comparisons of perinatal and infant mortality: population based retrospective study
Objectives To examine variations in the registration of extremely low birthweight and early gestation births and to assess their effect on perinatal and infant mortality rankings of industrialised countries
No Ending Point in The Bragg-to-Vortex Glass Phase Transition Line at Low Temperatures
We have measured the magnetic hysteresis loops and the magnetic relaxation
for (Bi-2212) single crystals which exhibit the
second magnetization peak effect. Although no second peak effect is observed
below 20 K in the measurement with fast field sweeping rate, it is found that
the second peak effect will appear again after long time relaxation or in a
measurement with very slow field sweeping rate at 16 K. It is anticipated that
the peak effect will appear at very low temperatures (approaching zero K) when
the relaxation time is long enough. We attribute this phenomenon to the profile
of the interior magnetic field and conclude that the phase transition line of
Bragg glass to vortex glass has no ending point at low temperatures.Comment: 4 pages, 5 figure
Electron-Spin Excitation Coupling in an Electron Doped Copper Oxide Superconductor
High-temperature (high-Tc) superconductivity in the copper oxides arises from
electron or hole doping of their antiferromagnetic (AF) insulating parent
compounds. The evolution of the AF phase with doping and its spatial
coexistence with superconductivity are governed by the nature of charge and
spin correlations and provide clues to the mechanism of high-Tc
superconductivity. Here we use a combined neutron scattering and scanning
tunneling spectroscopy (STS) to study the Tc evolution of electron-doped
superconducting Pr0.88LaCe0.12CuO4-delta obtained through the oxygen annealing
process. We find that spin excitations detected by neutron scattering have two
distinct modes that evolve with Tc in a remarkably similar fashion to the
electron tunneling modes in STS. These results demonstrate that
antiferromagnetism and superconductivity compete locally and coexist spatially
on nanometer length scales, and the dominant electron-boson coupling at low
energies originates from the electron-spin excitations.Comment: 30 pages, 12 figures, supplementary information include
Influence of rotational distortions on Li<sup>+</sup>-Â and Na<sup>+</sup>- intercalation in anti-NASICON Fe<sub>2</sub>(MoO<sub>4</sub>)<sub>3</sub>
Anti-NASICON
Fe<sub>2</sub>(MoO<sub>4</sub>)<sub>3</sub> (<i>P</i>2<sub>1</sub>/<i>c</i>) shows significant structural
and electrochemical differences in the intercalation of Li<sup>+</sup> and Na<sup>+</sup> ions. To understand the origin of this behavior,
we have used a combination of in situ X-ray and high-resolution neutron
diffraction, total scattering, electrochemical measurements, density
functional theory calculations, and symmetry-mode analysis. We find
that for Li<sup>+</sup>-intercalation, which proceeds via a two-phase
monoclinic-to-orthorhombic (<i>Pbcn</i>) phase transition,
the host lattice undergoes a concerted rotation of rigid polyhedral
subunits driven by strong interactions with the Li<sup>+</sup> ions,
leading to an ordered lithium arrangement. Na<sup>+</sup>-intercalation,
which proceeds via a two-stage solid solution insertion into the monoclinic
structure, similarly produces rotations of the lattice polyhedral
subunits. However, using a combination of total neutron scattering
data and density functional theory calculations, we find that while
these rotational distortions upon Na<sup>+</sup>-intercalation are
fundamentally the same as for Li<sup>+</sup>-intercalation, they result
in a far less coherent final structure, with this difference attributed
to the substantial difference between the ionic radii of the two alkali
metals
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