Universal Properties of Cuprate Superconductors: T_c Phase Diagram, Room-Temperature Thermopower, Neutron Spin Resonance, and STM Incommensurability Explained in Terms of Chiral Plaquette Pairing

We report that four properties of cuprates and their evolution with doping are consequences of simply counting four-site plaquettes arising from doping, (1) the universal T_c phase diagram (superconductivity between ~0.05 and ~0.27 doping per CuO_2 plane and optimal T_c at ~0.16), (2) the universal doping dependence of the room-temperature thermopower, (3) the superconducting neutron spin resonance peak (the “41 meV peak”), and (4) the dispersionless scanning tunneling conductance incommensurability. Properties (1), (3), and (4) are explained with no adjustable parameters, and (2) is explained with exactly one. The successful quantitative interpretation of four very distinct aspects of cuprate phenomenology by a simple counting rule provides strong evidence for four-site plaquette percolation in these materials. This suggests that inhomogeneity, percolation, and plaquettes play an essential role in cuprates. This geometric analysis may provide a useful guide to search for new compositions and structures with improved superconducting properties

Frequency and phase modulation performance of an injection-locked CW magnetron.

It is demonstrated that the output of a 2.45-GHz magnetron operated as a current-controlled oscillator through its pushing characteristic can lock to injection signals in times of the order of 100-500 ns depending on injection power, magnetron heater power, load impedance, and frequency offset of the injection frequency from the natural frequency of the magnetron. Accordingly, the magnetron can follow frequency and phase modulations of the injection signal, behaving as a narrow-band amplifier. The transmission of phase-shift-keyed data at 2 Mb/s has been achieved. Measurements of the frequency response and anode current after a switch of phase as a function of average anode current and heater power give new insight into the locking mechanisms and the noise characteristics of magnetrons

Harmonic analysis of irradiation asymmetry for cylindrical implosions driven by high-frequency rotating ion beams

Cylindrical implosions driven by intense heavy ions beams should be instrumental in a near future to study High Energy Density Matter. By rotating the beam by means of a high frequency wobbler, it should be possible to deposit energy in the outer layers of a cylinder, compressing the material deposited in its core. The beam temporal profile should however generate an inevitable irradiation asymmetry likely to feed the Rayleigh-Taylor instability (RTI) during the implosion phase. In this paper, we compute the Fourier components of the target irradiation in order to make the junction with previous works on RTI performed in this setting. Implementing a 1D and 2D beam models, we find these components can be expressed exactly in terms of the Fourier transform of the temporal beam profile. If $T$ is the beam duration and $\Omega$ its rotation frequency, "magic products" $\Omega T$ can be identified which cancel the first harmonic of the deposited density, resulting in an improved irradiation symmetry.Comment: 19 pages, 8 figures, to appear in PR

The ferroelectric and cubic phases in BaTiO_3 ferroelectrics are also antiferroelectric

Using quantum mechanics (QM, Density Functional Theory) we show that all four phases of barium titanate (BaTiO3) have local Ti distortions toward (an octahedral face). The stable rhombohedral phase has all distortions in phase (ferroelectric, FE), whereas higher temperature phases have antiferroelectric coupling (AFE) in one, two, or three dimensions (orthorhombic, tetragonal, cubic). This FE–AFE model from QM explains such puzzling aspects of these systems as the allowed Raman excitation observed for the cubic phase, the distortions toward observed in the cubic phase using x-ray fine structure, the small transition entropies, the heavily damped soft phonon modes, and the strong diffuse x-ray scattering in all but the rhombohedral phase. In addition, we expect to see additional weak Bragg peaks at the face centers of the reciprocal lattice for the cubic phase. Similar FE–AFE descriptions are expected to occur for other FE materials. Accounting for this FE–AFE nature of these phases is expected to be important in accurately simulating the domain wall structures, energetics, and dynamics, which in turn may lead to the design of improved materials

Reply to “Comment on ‘Phase diagram of MgO from density-functional theory and molecular-dynamics simulations’”

In answer to a Comment by Belonoshko [Phys. Rev. B 63, 096101 (2001)], we show that the B1-liquid melting curve of MgO obtained using two-phase simulations is in good agreement with the published one obtained using the Clausius-Clapeyron equation in conjunction with separate single phase calculations of liquid and solid

Crystal structure of 3-{(E)-[(3, 4-dichloro-phenyl)imino]methyl}benzene-1, 2-diol

The authors acknowledge the provision of funds for the purchase of diffractometer and encouragement by Dr.Muhammad Akram Chaudhary, Vice Chancellor, University of Sargodha, Pakistan.Peer reviewedPublisher PD

Morse stretch potential charge equilibrium force field for ceramics: Application to the quartz-stishovite phase transition and to silica glass

To predict phase transitions in ceramics and minerals from molecular dynamics simulations, we have developed a force field in which the charges are allowed to readjust instantaneously to the atomic configurations. These charges are calculated using the charge equilibration (QEq) method. In addition to electrostatics, a two-body Morse stretch potential is included to account for short-range nonelectrostatic interactions. This MS-Q potential is applied herein to SiO_2, where we find that it describes well the fourfold coordinated and sixfold coordinated systems (such as quartz and stishovite), silica glass, and the pressure-induced phase transition from quartz to stishovite

Studies of fullerenes and carbon nanotubes by an extended bond order potential

We present a novel approach to combine bond order potentials with long-range nonbond interactions. This extended bond order potential consistently takes into account bond terms and nonbond terms. It not only captures the advantages of the bond order potentials (i.e. simulating bond forming and breaking), but also systematically includes the nonbond contributions to energy and forces in studying the structure and dynamics of covalently bonded systems such as graphite, diamond, nanotubes, fullerenes and hydrocarbons, in their crystal and melt forms. Using this modified bond order potential, we studied the structure and thermal properties (including thermal conductivity) of C60 crystal, and the elastic properties and plastic deformation processes of the single-walled and double-walled nanotubes. This extended bond order potential enables us to simulate large deformations of a nanotube under tensile and compressive loads. The basic formulation in this paper is transferable to other bond order potentials and traditional valence force fields