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881.
Recent theories predict dissipationless spin current induced by an electric field in doped semiconductors. Nevertheless, the charge current is still dissipative in these systems. In this work, we theoretically predict the dissipationless spin-Hall effect, without any accompanying charge current, in some classes of band insulators, including zero-gap semiconductors such as HgTe and narrow-gap semiconductors such as PbTe. This effect is similar to the quantum-Hall effect in that all the states below the gap contribute and there occurs no dissipation. However, the spin-Hall conductance is not quantized even in two dimensions. This is the first example of a nontrivial topological structure in a band insulator without any magnetic field. 相似文献
882.
The Ru3(CO)12-catalyed cross-coupling reaction of esters with organoboron compounds leading to ketones is described. A wide variety of functional groups can be tolerated under the reaction conditions. Aromatic boronates function as a coupling partner to give aryl ketones. Acyl-alkyl coupling to dialkyl ketones is also achieved by the use of 9-alkyl-9-BBN in place of boronates. The Ru3(CO)12-catalyzed decarbonylative reduction of esters with ammonium formate (HCOONH4) leading to hydrocarbons is also described. No expected aldehydes are produced, and controlled experiments indicate that aldehydes are not intermediate for the transformation. A hydrosilane can also be used as a reducing reagent in place of HCOONH4. A wide variety of functional groups are compatible for both reactions. The key step for both catalytic reactions is the directing group-promoted cleavage of an acyl carbon-oxygen bond in esters, leading to the generation of acyl transition metal alkoxo complexes. 相似文献
883.
We propose a method for all-fiber ultra-fast switching using stimulated Raman scattering. It is based on the transference of energy from the signal as pump to the control signal as first Stokes by stimulated Raman scattering. In the absence of a control signal, the transference of energy from the pump signal to the generated first Stokes is negligible, which results in high output power at the pump signal wavelength. To minimize the walk-off problem between two wavelengths, we chose pump signal and control signal to be equally spaced on opposite sides of the zero dispersion wavelength of the fiber. Based on this assumption, the all-fiber ultra-fast optical switch with low power consumption and high output extinction ratio can be realized. 相似文献
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Ohne Zusammenfassung 相似文献
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Ohne Zusammenfassung 相似文献
889.
Michio Sorai Masanori Yoshikawa Naoto Arai Hiroshi Suga Syûzô Seki 《Journal of Physics and Chemistry of Solids》1978,39(4):413-425
The heat capacity of the tetranuclear nickel cluster complex, tetrakis [μ3-methoxo-2,4-pentanedionato (methanol) nickel (2)], has been measured from 0.4 to 285 K. Contrary to the previous prediction by Bertrand et al.[6], that this complex exhibits an intercluster ferromagnetic spin coupling, the present heat capacity measurement shows no indication of the spin-ordering effect caused by the intercluster interaction at least down to 0.4 K. Instead, a heat capacity anomaly centered around 1.5 K with a shoulder at 0.5 K has been observed. This anomaly is well accounted for in terms of both a level splitting of the ground S = 4 state due to a uni-axial crystalline anisotropy and a tunnel-splitting of the rotational levels of methyl groups. The intracluster spin exchange constant J and the single-ion zero-field splitting parameter D are determined to be and (h being the Planck constant and c the speed of light in a vacuum). The temperature dependence of the effective Bohr magneton [6] is also satisfactorily accounted for on the basis of this model. The tunnel-splitting δ of the lowest rotational level of the four methyl groups belonging to methoxides is estimated to be and the corresponding potential barrier Vo is found to be Vo = 1.9–1.5 kJmol?1. 相似文献
890.
Kyung-Han Jung Jong-Won Yoon Naoto Koshizaki Young-Soo Kwon 《Current Applied Physics》2008,8(6):761-765
Au/SiO2 nanocomposite films were prepared on Si wafers by cosputtering of SiO2 and gold wires. Au/Si atomic ratios in Au/SiO2 nanocomposite films were varied from 0.53 to 0.92 by controlling the length of gold wire to study the evolution of the crystallization of gold, the size of Au/SiO2 nanocomposite particles, and the optical properties of as-deposited Au/SiO2 nanocomposite films. An X-ray photoelectron spectroscopy reveals that Au exists as a metallic phase in the bulk of SiO2 matrix. Dome-shaped Au/SiO2 nanocomposite particles and both Au (1 1 1) and (2 0 0) planes were observed in a field-emission scanning electron microscopy and X-ray diffraction studies respectively. With an ultraviolet-visible, absorption peaks of Au/SiO2 nanocomposite films were observed at 525 nm. 相似文献