Asymmetric transport due to spin injection into a Kondo alloy

Spin injection is found to have a significant effect on the transport properties of the Kondo alloy Cu(Fe). When a spin-polarized electron current flows from Co into Cu(Fe) wires through the Co/Cu(Fe) interface, the resistivity of the Cu(Fe) wire is suppressed near the interface, as distinct from the ordinary logarithmic increase in the resistivity at low temperatures. For the opposite current direction, no significant changes are observed. The asymmetry of the resistivity with respect to the current direction decays with a characteristic length of 1.5+/-0.4 microm at 2.5 K as the distance from the interface is increased. Possible mechanisms for the asymmetry are discussed.     

Photosensitivity of As2S3 chalcogenide thin films at 1.5 microm

Chalcogenide glasses are promising candidates for all-optical switching and various nonlinear applications. However, we show that As2S3 thin films are photosensitive at wavelengths in the 1.5-microm telecommunication window. This sensitivity is evidenced by the formation of self-written waveguides in slabs, where channels as narrow as 1 microm are created. We also show the detrimental effects of such photosensitivity in ridge waveguides. This photosensitivity seems to occur only in thin-film form and not in bulk samples or fibers.     

59Co, 23Na NMR and electric field gradient calculations in the layered cobalt oxides NaCoO2 and HCoO2

⁵⁹Co and ²³Na NMR has been applied to the layered cobalt oxides NaCoO₂ and HCoO₂ at three different magnetic field strengths (4.7, 7.1 and 11.7 T). The ⁵⁹Co and ²³Na quadrupole and anisotropic shift tensors have been determined by iterative fitting of the NMR line shapes at the three magnetic field strengths. Due to the large ⁵⁹Co quadrupole interaction in NaCoO₂, a frequency-swept irradiation procedure was used to alleviate the limited bandwidth of the excitation. While the ⁵⁹Co and ²³Na shift and quadrupole coupling tensors in NaCoO₂ are found to be coincident and axially symmetric in agreement with the crystal symmetry requirements, the fits of the ⁵⁹Co NMR spectra clearly show the presence of structural disorder in HCoO₂. The ²³Na chemical shift anisotropy can be reproduced by shift tensor calculations using a point dipole model and considering that the magnetic susceptibility in NaCoO₂ is due to Van Vleck paramagnetism for Co³⁺. Electric field gradient calculations using either the empirical point charge model or the ab initio full potential-linearized augmented plane wave method are compared with the experimental NMR data.     

2H( 3He, t)2p reaction at 2 GeV

The exclusive ²H( ³He, t)2p reaction has been studied at 2 GeV for energy transfers up to 500 MeV and triton angles up to 3.4^°. The protons were measured in the large acceptance magnetic detector DIOGENE, in coincidence with the forward tritons detected in a dedicated magnetic arm. The energy transfer spectra extend well above the pion threshold. However, in the region of Δ excitation, the yield is less than 10% of the inclusive ²H( ³He, t) cross-section, which indicates the small contribution of the ΔN ↦ NN process. The angular distributions of the two protons in their center of mass have been analysed as a function of energy transfer and triton angle and a Legendre polynomial decomposition has been achieved. These data have been compared to a model based on a coupled-channel approach for describing the NN and NΔ systems. Received: 21 October 2002 / Accepted: 15 November 2002 / Published online: 11 March 2003 RID="a" ID="a"e-mail: ramstein@ipno.in2p3.fr RID="†" ID="†"Deceased. RID="†" ID="†"Deceased. RID="d" ID="d"Present adress: School of Engineering, J?nk?ping University, P.O. Box 1026, S-551 11 J?nk?ping, Sweden. Communicated by M. Gar?on     

MIL-103, a 3-D lanthanide-based metal organic framework with large one-dimensional tunnels and a high surface area

A lanthanide-based metal organic framework, formulated Tb(C27H15O6)(H2O).2C6H11OH, has been solvothermally synthesized using the extended rigid tritopic ligand 1,3,5-tribenzoate. Included free solvent could be removed upon heating, and the resulting material presents large 1-D micropores (free diameter = 10 A) and a high surface area (SLangmuir > 1000 m2.g-1).     

Isolation and low-temperature x-ray analysis of intramolecular triarylmethane-triarylmethylium complex: preference for a C-H-bridged unsymmetric structure exhibiting a facile 1,5-hydride shift and charge-transfer interaction

The intramolecular triarylmethane-methylium complex with an averaged C2v-symmetry was successfully generated by N-methylation of the acridine-acridan hybrid. Theoretical calculation and VT-NMR analyses in solution indicate the unsymmetric geometry for the three-center bond, which was finally confirmed crystallographically. Significant degree of CT interaction is induced through the very short C-H...C+ contact.     

Theory of tunnel ionization in complex systems

A quasianalytical theory of tunnel ionization is developed that is applicable to general complex systems, such as large molecules. Our analysis reveals strong deviations from conventional tunnel ionization theories, dependent upon the system's geometry, angular momentum, and polarizability. A comparison of our theory with recent C(60) ionization experiments yields reasonable agreement.     

Evanescent-wave mirror for ultracold diatomic polar molecules

We describe the interaction of an ultracold diatomic polar molecule with an evanescent-wave mirror. Several features of this system are explored, such as the coupling between internal rovibrational states of the molecule and the laser field. Numerical simulations show quantum reflection and state selection under attainable physical conditions. Such molecular optics components will facilitate the manipulation and trapping of ultracold molecules, and might serve in future applications in several fields, e.g., as devices to filter and select a state for ultracold chemistry, to measure extremely low temperatures of molecules, or to manipulate states for quantum information processing.     

Electronic origin of disorder and diffusion at a molecule-metal interface: self-assembled monolayers of CH3S on Cu111

The relationship between structure, interfacial electrostatics, bonding, and dynamics of organic molecules on metals is studied using a self-assembled monolayer of methylthiolate, CH3S, on Cu(111). The flat adsorption energy landscape of CH(3)S/Cu(111) results from metal-to-molecule charge redistribution which allows for a high mobility of CH3S. This contributes a nonuniform diffuse background to Bragg scattering, which needs to be considered in diffraction analyses. Ramifications on the interpretation of experimental data and the potential impact on the design of metal-organic interfaces are discussed.     

Spatial distribution of cold antihydrogen formation

Antihydrogen is formed when antiprotons are mixed with cold positrons in a nested Penning trap. We present experimental evidence, obtained using our antihydrogen annihilation detector, that the spatial distribution of the emerging antihydrogen atoms is independent of the positron temperature and axially enhanced. This indicates that antihydrogen is formed before the antiprotons are in thermal equilibrium with the positron plasma. This result has important implications for the trapping and spectroscopy of antihydrogen.