38 research outputs found
Magnetic-field-enhanced incommensurate magnetic order in the underdoped high-temperature superconductor YBa(2)Cu(3)O(6.45)
We present a neutron-scattering study of the static and dynamic spin
correlations in the underdoped high-temperature superconductor
YBa(2)Cu(3)O(6.45) in magnetic fields up to 15 T. The field strongly enhances
static incommensurate magnetic order at low temperatures and induces a
spectral-weight shift in the magnetic-excitation spectrum. A reconstruction of
the Fermi surface driven by the field-enhanced magnetic superstructure may thus
be responsible for the unusual Fermi surface topology revealed by recent
quantum-oscillation experiments.Comment: 4 pages, 3 figures. Version 2 as accepted by PRL, contains updated
reference list and improved comparison to similar effects in the La-214
syste
Giant phonon anomalies and central peak due to charge density wave formation in YBaCuO
The electron-phonon interaction is a major factor influencing the competition
between collective instabilities in correlated-electron materials, but its role
in driving high-temperature superconductivity in the cuprates remains poorly
understood. We have used high-resolution inelastic x-ray scattering to monitor
low-energy phonons in YBaCuO (superconducting
K), which is close to a charge density wave (CDW) instability. Phonons in a
narrow range of momentum space around the CDW ordering vector exhibit extremely
large superconductivity-induced lineshape renormalizations. These results imply
that the electron-phonon interaction has sufficient strength to generate
various anomalies in electronic spectra, but does not contribute significantly
to Cooper pairing. In addition, a quasi-elastic "central peak" due to CDW
nanodomains is observed in a wide temperature range above and below ,
suggesting that the gradual onset of a spatially inhomogeneous CDW domain state
with decreasing temperature is a generic feature of the underdoped cuprates
Progress in Neutron Scattering Studies of Spin Excitations in High-Tc Cuprates
Neutron scattering experiments continue to improve our knowledge of spin
fluctuations in layered cuprates, excitations that are symptomatic of the
electronic correlations underlying high-temperature superconductivity.
Time-of-flight spectrometers, together with new and varied single crystal
samples, have provided a more complete characterization of the magnetic energy
spectrum and its variation with carrier concentration. While the spin
excitations appear anomalous in comparison with simple model systems, there is
clear consistency among a variety of cuprate families. Focusing initially on
hole-doped systems, we review the nature of the magnetic spectrum, and
variations in magnetic spectral weight with doping. We consider connections
with the phenomena of charge and spin stripe order, and the potential
generality of such correlations as suggested by studies of magnetic-field and
impurity induced order. We contrast the behavior of the hole-doped systems with
the trends found in the electron-doped superconductors. Returning to hole-doped
cuprates, studies of translation-symmetry-preserving magnetic order are
discussed, along with efforts to explore new systems. We conclude with a
discussion of future challenges.Comment: revised version, to be published in JPSJ, 20 pages, 21 figure
Characterisation of the polarisation state of embedded piezoelectric transducers by thermal waves and thermal pulses
In this work, we apply the thermal wave method and the thermal pulse method
for non-destructive characterisation of the polarisation state of embedded
piezoelectric transducers. Heating the sample with a square-wave modulated
laser beam or a single laser pulse leads to a pyroelectric current recorded
in the frequency or time domain, respectively. It carries information about
the polarisation state. Analytical and numerical finite element models
describe the pyroelectric response of the piezoceramic. Modelling and
experimental results are compared for a simple lead–zirconate–titanate (PZT)
plate, a low-temperature co-fired ceramics (LTCC)/PZT sensor and
actuator,
and a macro-fibre composite (MFC) actuator
Principles for Controlling the Electronic Quality of High-Rate Deposited a-Si:H Films
By altering the plasma generation frequency, applying a magnetic field, changing the plasma regime from the low voltage γ-regime where the dominant electron-energy gain mechanism is related to the sheath expansion, to the high voltage γ-regime where the discharge is maintained by secondary electrons emitted by the electrodes under ion bombardment, or generating a highly excited low-pressure plasma in a helicon-type source the influence of the particle and energy flux to the substrate on the a-Si:H film electronic properties was investigated. Deposition rate simulation was performed regarding a radical source located at the sheath/plasma boundary. Radical losses due to diffusion and reactive collisions with gas molecules were taken into account
Incommensurate magnetic order and dynamics induced by spinless impurities in YBa₂Cu₃O<sub>6.6</sub>
We report an inelastic-neutron-scattering and muon-spin-relaxation study of the effect of 2% spinless (Zn) impurities on the magnetic order and dynamics of YBa₂Cu₃O6.6, an underdoped high-temperature superconductor that exhibits a prominent spin pseudogap in its normal state. Zn substitution induces static magnetic order at low temperatures and triggers a large-scale spectral-weight redistribution from the magnetic resonant mode at 38 meV into uniaxial, incommensurate spin excitations with energies well below the spin pseudogap. These observations indicate a competition between incommensurate magnetic order and superconductivity close to a quantum critical point. Comparison to prior data on La2-xSrxCuO₄ suggests that this behavior is universal for the layered copper oxides and analogous to impurity-induced magnetic order in one-dimensional quantum magnets
A Laser Intensity Modulation Method for the Evaluation of the Polarization State of Embedded Piezoceramics
Tunneling conduction mechanisms in strontium ferromolybdate ceramics with strontium molybdate dielectric intergrain barriers
This work is a contribution to the understanding of the electrical resistivity in strontium ferromolybdate (Sr2FeMoO6-δ, SFMO) ceramics. It demonstrates that an appropriate thermal treatment leads to the formation of dielectric SrMoO4 shells at the surface of SFMO nanograins. In samples without SrMoO4 shells, the sign of the temperature coefficient of resistance changes with increasing temperature from negative at very low temperatures to positive at higher temperatures. Samples exhibiting a negative temperature coefficient contain SrMoO4 shells and demonstrate a behavior of the resistivity that can be described in terms of the fluctuation-induced tunneling model, and near room temperature the conductivity mechanism converts to a variable-range hopping one. The results of this work serve as a starting point for the understanding of the low-field magnetoresistance which is very promising for spintronic device application.publishe