Hydrogen-bonded dimer of N,N′-(5-n-butyl-5-oxodibenzo[b,d]phosphole-3,7-diyl)bis(benzamide) dimethylformamide solvate

The structure of a large wing-span phosphine, in the oxide form, N,N-(5-n-butyl-5-oxodibenzo[b,d]phosphole-3,7-diyl)bis(benzamide), C₃₀H₂₇N₂O₃P, cocrystallized with dimethylformamide (DMF), C₃H₇NO, is reported. The title compound is crystallized in a triclinic system with cell dimensions of a = 10.295(8) b = 12.743(5) c = 13.239(6) Å, = 108.14(3), = 108.16(5), = 101.20(4)°, and V=1484.4(5) ų, and forms a hydrogen-bonded dimer via two hydrogen bond linkages of the P—O ··· H—N type involving one of the two amide groups.     

Scattering of simple harmonic waves by a circular cavity in a fluid-infiltrated poro-elastic medium

Scattering by a cylindrical cavity in a porous solid is studied by the boundary layer approximation of Mei and Foda. Quantitative results will be presented for two cases: (1) vacuum cavity and (2) cavity filled with fluid. In each case both P and SV incident waves will be studied. Focus will be on the stress distribution near the cavity surface and contrast to the non-porous case will be pointed out. The effect of fluid compressibility due to possible entrainment of air will be discussed. These results should be of interest to the design of long tunnels subject to earthquakes.     

The Probability Content of Cones in Isotropic Random Fields

This paper provides computable representations for the evaluation of the probability content of cones in isotropic random fields. A decomposition of quadratic forms in spherically symmetric random vectors is obtained and a representation of their moments is derived in terms of finite sums. These results are combined to obtain the distribution function of quadratic forms in spherically symmetric or central elliptically contoured random vectors. Some numerical examples involving the sample serial covariance are provided. Ratios of quadratic forms are also discussed.     

Magnetic order and spin dynamics in ferroelectric HoMnO3

Hexagonal HoMnO3 is a frustrated antiferromagnet (T(N)=72 K) ferroelectric (T(C)=875 K) in which these two order parameters are coupled. Our neutron measurements of the spin-wave dispersion for the S=2 Mn3+ on the layered triangular lattice are well described by a two-dimensional nearest-neighbor Heisenberg exchange J=2.44 meV, and an anisotropy D that is 0.28 meV above the spin-reorientation transition at 40 K and 0.38 meV below. For H parallel c the magnetic structures and phase diagram have been determined, and reveal additional transitions below 8 K where the ferroelectrically displaced Ho3+ ions are ordered magnetically.     

d-d excitations in manganites probed by resonant inelastic x-ray scattering

We report a study of electronic excitations in manganites exhibiting a range of ground states, using resonant inelastic x-ray scattering (RIXS) at the Mn K edge. Excitations with temperature dependent changes correlated with the magnetism were observed as high as 10 eV. By calculating Wannier functions, and finite-q response functions, we associate this dependence with intersite d-d excitations. The calculated dynamical structure factor is found to be similar to the RIXS spectra.     

Direct observation of large electronic domains with memory effect in doped manganites

We use a spatially resolved, direct spectroscopic probe for electronic structure with an additional sensitivity to chemical compositions to investigate high-quality single crystal samples of La(1/4)Pr(3/8)Ca(3/8)MnO3, establishing the formation of distinct insulating domains embedded in the metallic host at low temperatures. These domains are found to be at least an order of magnitude larger in size compared to previous estimates and exhibit memory effects on temperature cycling in the absence of any perceptible chemical inhomogeneity, suggesting long-range strains as the probable origin.     

Spin singlet formation in MgTi2O4: evidence of a helical dimerization pattern

The transition-metal spinel MgTi2O4 undergoes a metal-insulator (M-I) transition on cooling below T(M-I)=260 K. A sharp reduction of the magnetic susceptibility below T(M-I) suggests the onset of a magnetic singlet state. Using high-resolution synchrotron and neutron powder diffraction, we have solved the low-temperature crystal structure of MgTi2O4, which is found to contain dimers with short Ti-Ti distances (the locations of the spin singlets) alternating with long bonds to form helices. Band structure calculations based on hybrid exchange density functional theory show that, at low temperatures, MgTi2O4 is an orbitally ordered band insulator.     

Exchange interaction effects on the optical properties of LuMnO3

We have measured the optical conductivity of single crystal LuMnO3 from 10 to 45000 cm(-1) at temperatures between 4 and 300 K. A symmetry allowed on-site Mn d-d transition near 1.7 eV is observed to blueshift ( approximately 0.1 eV) in the antiferromagnetic state due to Mn-Mn superexchange interactions. Similar anomalies are observed in the temperature dependence of the TO phonon frequencies which arise from spin-phonon interaction. We find that the known anomaly in the temperature dependence of the quasistatic dielectric constant epsilon(0) below T(N) approximately 90 K is overwhelmingly dominated by the phonon contributions.     

Coherent manipulation of electronic States in a double quantum dot

We investigate coherent time evolution of charge states (pseudospin qubit) in a semiconductor double quantum dot. This fully tunable qubit is manipulated with a high-speed voltage pulse that controls the energy and decoherence of the system. Coherent oscillations of the qubit are observed for several combinations of many-body ground and excited states of the quantum dots. Possible decoherence mechanisms in the present device are also discussed.