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 YBa2_2Cu3_3O6.6_{6.6}

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 YBa$_2$Cu$_3$O$_{6.6}$ (superconducting $\bf T_c = 61$ 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 $\bf T_c$, 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_6.6

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

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