Mott-Anderson transition controlled by a magnetic field in pyrochlore molybdate

The pyrochlore molybdate Gd2MO2O7 locates near the phase boundary between the ferromagnetic-metallic and the spin-glass insulating state. This metal-insulator transition is governed on a large energy scale by the electron-correlation effect, while the geometrical frustration causes the random potential. The magnetic field can tune the randomness of the potential and control, under a suitable pressure, the continuous Mott-Anderson transition precisely. The critical exponent (mu = 1.04 +/- 0.1) of the Mott-Anderson transition has been determined for this ferromagnetic orbital-degenerate electron system.     

Anomalous pressure dependence of the superconducting transition temperature of beta-pyrochlore AOs2O6 oxides

High-pressure effects on the superconducting transitions of beta-pyrochlore oxide superconductors AOs(2)O(6) (A = Cs,Rb,K) are studied by measuring resistivity under high pressures up to 10 GPa. The superconducting transition temperature T(c) first increases with increasing pressure in every compound and then exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa), and 10 K (0.6 GPa) for A = Cs, Rb, and K, respectively. Finally, the superconductivity is suppressed completely at a critical pressure near 7 GPa and 6 GPa for A = Rb and K and probably above 10 GPa for A = Cs. Characteristic changes in the coefficient A of the T(2) term in resistivity and residual resistivity are observed, both of which are synchronized with the corresponding change in T(c).     

Spin, charge, and orbital ordering in La0.5Sr1.5Mno4

We have analyzed the experimental evidence of charge and orbital ordering in La0.5Sr1.5MnO4 using first principles band structure calculations. Our results suggest the presence of two types of Mn sites in the system. One of the Mn sites behaves as an Mn3+ ion, favoring a Jahn-Teller distortion of the surrounding oxygen atoms, while the distortion around the other is not a simple breathing mode kind. Band structure effects are found to dominate the experimental spectrum for orbital and charge ordering, providing an alternate explanation for the experimentally observed results.     

Total energy method from many-body formulation

The fruitfulness of traditional many-body Green's function theory for calculating the total energy of real systems is demonstrated using the random phase approximation in the Luttinger-Ward formulation. As the first application to a real system, the total energy of H2 is calculated as a function of nuclear separation and compared with the configuration interaction and the local density approximation results. While the local density result is in large error for large separations, the present approach gives satisfactory agreement with the configuration interaction results. The method is promising as an alternative to the quantum Monte Carlo technique.     

First-principles molecular-dynamics simulations of a hydrated electron in normal and supercritical water

A first principles study of a hydrated electron in water at ordinary and supercritical conditions is presented. In the first case, the electron cleaves a cavity in the hydrogen bond network in which six H2O molecules form the solvation shell. The electron distribution assumes an ellipsoidal shape, and the agreement of the computed and the experimental optical absorption seems to support this picture. At supercritical conditions, instead, the H-bond network is not continuous and allows us to predict that the electron localizes in preexisting cavities in a more isotropic way. Four water molecules form the solvation shell but the localization time shortens significantly.     

Structure of an antitumor antibiotic,reductiomycin

The structure of an antitumor antibiotic isolated from a variant of $\text{Streptomyces orientalis}$ was established as ($\text{1}$) by chemical and spectral evidence. The antibiotic was found to be identical with reductiomycin, and therefore the structure (X) of reductiomycin previously reported must be revised.     

A new method for cleavage of aliphatic methyl ethers

A new efficient procedure for the cleavage of aliphatic methyl ethers under the mild conditions by the use of the reagents system, boron tribromide - sodium iodide - 15-crown-5 is described.     

Hyperfine field of positive muon in ferromagnetic nickel

The electronic structure around a positive muon μ⁺ at an octahedral interstitial site of a ferromagnetic nickel is calculated from first principles. The hyperfine field experienced by μ⁺ at absolute zero is calculated to be ?0.72 kG in satisfactory agreement with the experimental value of ?0.64 kG. The calculation also explains the temperature dependence of the hyperfine field. It is shown that the temperature dependence of the hyperfine field coupling constant A(T) is predominantly determined by single particle excitations.