Electron paramagnetic resonance shift in II1-xMnxVI diluted magnetic semiconductors in the presence of strong exchange coupling

Electron paramagnetic resonance (EPR) has been investigated in two II1-xMnxVI alloys--Cd1-xMnxSe and Cd1-xMnxS--for a series of high Mn concentrations and at low temperatures T, i.e., under conditions where the spin subsystems in these materials are strongly coupled. We have observed a very significant shift of the resonance field from the EPR position of Mn2+ ions that increases with increasing x and with decreasing T. Furthermore, the use of multiple frequencies has allowed us to attribute the observed shift to an internal field that originates from the spin sublattice within the II1-xMnxVI host.     

On splitting of totally singular quadratic forms

In this note we completely study the standard splitting of quasi-Pfister forms and their neighbors, and we include some general results on standard splitting towers of totally singular quadratic forms. The author was supported by the European research network HPRN-CT-2002-00287 “AlgebraicK-Theory, Linear Algebraic Groups and Related Structures”.     

Measurement of the total active 8B solar neutrino flux at the Sudbury Neutrino Observatory with enhanced neutral current sensitivity

The Sudbury Neutrino Observatory has precisely determined the total active (nu(x)) 8B solar neutrino flux without assumptions about the energy dependence of the nu(e) survival probability. The measurements were made with dissolved NaCl in heavy water to enhance the sensitivity and signature for neutral-current interactions. The flux is found to be 5.21 +/- 0.27(stat)+/-0.38(syst) x 10(6) cm(-2) s(-1), in agreement with previous measurements and standard solar models. A global analysis of these and other solar and reactor neutrino results yields Deltam(2)=7.1(+1.2)(-0.6) x 10(-5) eV(2) and theta=32.5(+2.4)(-2.3) degrees. Maximal mixing is rejected at the equivalent of 5.4 standard deviations.     

Theory of insulator metal transition and colossal magnetoresistance in doped manganites

The persistent proximity of insulating and metallic phases, a puzzling characteristic of manganites, is argued to arise from the self-organization of the twofold degenerate e(g) orbitals of Mn into localized Jahn-Teller (JT) polaronic levels and broad band states due to the large electron-JT phonon coupling present in them. We describe a new two band model with strong correlations and a dynamical mean-field theory calculation of equilibrium and transport properties. These explain the insulator metal transition and colossal magnetoresistance quantitatively, as well as other consequences of two state coexistence.     

Metal Ion Complexation: A Route to 2 D Templates?

The two-dimensional ordering of a number of 2,2'-bipyridine derivatives at the liquid/solid interface has been investigated by scanning tunneling microscopy. By appropriate functionalization of the bipyridine units, their intermolecular distance can be tuned, which has proved to be crucial for complexation with metal ions. The in situ addition of metal salts (Pd(2+), Cu(2+)), leading to the formation of metal-bipyridine complexes, has a dramatic influence on the two-dimensional ordering of the molecules and suggests that these complexes could be used as templates.     

C2-symmetric diphosphinite ligands derived from carbohydrates. The strong influence of remote stereocenters on asymmetric rhodium-catalyzed hydrogenation

Modular ligands of C(2) symmetry (13a-e, 14a,b,d, and ent-9), systematically modified at positions 2 and 5, were easily prepared from d-glucosamine, D-glucitol, and tartaric acid, respectively. The application of these ligands in the rhodium-catalyzed hydrogenation of methyl acetamidoacrylate, methyl acetamidocinnamate, and dimethyl itaconate shows that both the configuration and the substituents at positions 2 and 5 of the tetrahydrofuran backbone have a strong influence on the enantioselectivty of the processes.