Zigzag edge modes in Z2 topological insulator: reentrance and completely flat spectrum

The spectrum and wave function of helical edge modes in Z_2 topological insulator are derived on a square lattice using Bernevig-Hughes-Zhang (BHZ) model. The BHZ model is characterized by a "mass" term M (k) that is parameterized as M (k) = Delta - B k^2. A topological insulator realizes when the parameters Delta and B fall on the regime, either 0 < Delta /B < 4 or 4 < Delta /B < 8. At Delta /B = 4, which separates the cases of positive and negative (quantized) spin Hall conductivities, the edge modes show a corresponding change that depends on the edge geometry. In the (1,0)-edge, the spectrum of edge mode remains the same against change of Delta /B, although the main location of the mode moves from the zone center for Delta /B < 4, to the zone boundary for Delta /B > 4 of the 1D Brillouin zone. In the (1,1)-edge geometry, the group velocity at the zone center changes sign at Delta /B = 4 where the spectrum becomes independent of the momentum, i.e. flat, over the whole 1D Brillouin zone. Furthermore, for Delta/B < 1.354..., the edge mode starting from the zone center vanishes in an intermediate region of the 1D Brillouin zone, but reenters near the zone boundary, where the energy of the edge mode is marginally below the lowest bulk excitations. On the other hand, the behavior of reentrant mode in real space is indistinguishable from an ordinary edge mode.Comment: 19 pages, 33 figure

Flat edge modes of graphene and of Z2 topological insulator

A graphene nano-ribbon in the zigzag edge geometry exhibits a specific type of gapless edge modes with a partly flat band dispersion. We argue that the appearance of such edge modes are naturally understood by regarding graphene as the gapless limit of a Z2 topological insulator. To illustrate this idea, we consider both Kane-Mele (graphene-based) and Bernevig-Hughes-Zhang models: the latter is proposed for HgTe/CdTe 2D quantum well. Much focus is on the role of valley degrees of freedom, especially, on how they are projected onto and determine the 1D edge spectrum in different edge geometries

Ion transfer and adsorption of water-soluble metal complexes of 8-hydroxyquinoline derivatives at the water|1,2-dichloroethane interface

金沢大学理工研究域物質化学系The transfer mechanism and adsorption state of water-soluble 8-quinolinolate complexes were studied at the water|1,2-dichloroethane interface by electrochemical and spectroelectrochemical techniques. The interfacial affinities of the metal complexes of 8-hydroxyquinoline-5-sulfonate (QS) were estimated as , > . Potential modulated fluorescence spectroscopy revealed the potential-driven process of fluorescent QS complexes, where Al(III) and Zn(II) complexes were transferred across the interface accompanied by the adsorption at the aqueous side of the interface. The adsorption state and preferential molecular orientation of these complexes were analyzed in detail by polarization-modulation total internal reflection fluorescence (PM-TIRF) spectroscopy. The PM-TIRF results showed that the square-planar 1:2 complexes, and , were oriented relatively in parallel to the interface and approximately identical to the aqueous species. The adsorption behavior of the Zn(II) complex of tridentate 8-hydroxyquinoline-2-carboxylate (QC) ligand was also investigated, and exhibited a strong interfacial affinity with intermediate spectral features between the aqueous and organic species.Embargo Period 12 monthsThis paper has a Supplementary material

Purification and characterization of UDP-glucose: hydroxycoumarin 7-O-glucosyltransferase, with broad substrate specificity from tobacco cultured cells

The enzyme UDP-glucose: hydroxycoumarin 7-O-glucosyltransferase (CGTase), which catalyzes the formation of scopolin from scopoletin, was purified approximately 1200-fold from a culture of 2,4-D-treated tobacco cells (Nicotiana tabacum L. cv. Bright Yellow T-13) with a yield of 7%. Purification to apparent homogeneity, as judged by SDS-PAGE, was achieved by sequential anion-exchange chromatography, hydroxyapatite chromatography, gel filtration, a second round of anion-exchange chromatography, and affinity chromatography on UDP-glucuronic acid agarose. The purified enzyme had a pH optimum of 7.5, an isoelectric point (pI) of 5.0, and a molecular mass of 49 kDa. The enzyme did not require metal cofactors for activity. Its activity was inhibited by Zn2+, Co2+ and Cu2+ ions, as well as by SH-blocking reagents. The K-m values for UDP-glucose, scopoletin and esculetin were 43, 150 and 25 mu M. respectively. A study of the initial rate of the reaction suggested that the reaction proceeded via a sequential mechanism. The purified enzyme preferred hydroxycoumarins as substrates but also exhibited significant activity with flavonoids. A database search using the amino terminus amino acid sequence of CGTase revealed strong homology to the amino acid sequences of other glucosyltransferases in plants.ArticlePlant Science. 157(1):105-112 (2000)journal articl

Heat Transport of Powder as the Subject of Cryogenic Insulation : 2nd Report, Heat Conduction under Vacuum

In the present work, an investigation was made on the heat transport through insulation powder evacuated under high vacuum, in which an aluminium powder was added for radiation shield. Experiments on heat flux in the powder were carried out from room temperature down to liquefied Belgium temperature, which enabled us to examine the relation between the heat flux and temperature. Furthermore, the general solution for total heat transfer for combined radiation and conduction proposed by Wang and Tien was applied to the powder, and was compared with the experimental results. We then quantitatively determined the roles of the contribution from both radiation and conduction and the effect of added aluminium powder, and investigated the basic heat transfer mechanism in the powder at low temperatures such as extinction coefficient for radiation and contact conduction between particles