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1
Topological Aspects and Transport Properties of Edge States in the Multi-band Superconductor Sr2RuO4

Yoshiki Imai,Katsunori Wakabayashi,Manfred Sigrist 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
Motivated by the spin-triplet superconductor Sr2RuO4, we investigate the edge states by using atwo-band tight-binding model with interorbital hybridization and spin-orbit coupling. In particularwe focus on the topological aspects and the transport properties in the chiral spin-triplet superconductingphase. The Fermi surfaces correspond to the ones of Sr2RuO4 where the and the bandshave hole- and electron-like characters, respectively. Although a full quasiparticle excitation gapis present in the bulk system, gapless edge states appear and affect both the spin and the chargecurrents. We study the interplay between electron- and hole-like particles in the formation of theseedge states and edge currents. Topologically the two bands compensate for each other such that theedge state is not topologically protected. The repulsive interaction yields a spin polarization nearthe edges and lifts the degeneracy of the subgap edge states. The net spontaneous magnetizationgenerated through both the edge charge current and the spin polarization may be small due to cancelingeffects. The lifting of the spin degeneracy could likely be detected by quasiparticle tunnelingfor the surface density of states.
2
Functional Reconstitution of Cellulose Synthase in Escherichia coli

Imai, Tomoya,Sun, Shi-jing,Horikawa, Yoshiki,Wada, Masahisa,Sugiyama, Junji American Chemical Society 2014 Biomacromolecules Vol.15 No.11
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Cellulose is a high molecular weight polysaccharide of β1 → 4-d-glucan widely distributed in naturefrom plant cell walls to extracellular polysaccharide in bacteria. Cellulose synthase, together with other auxiliary subunit(s) in the cell membrane, facilitates the fibrillar assembly of cellulose polymer chains into a microfibril. The gene encoding the catalytic subunit of cellulose synthase is cesA and has been identified in many cellulose-producing organisms. Very few studies, however, have shown that recombinant CesA protein synthesizes cellulose polymer, but the mechanism by which CesA protein synthesizes cellulose microfibrils is not known. Here we show that cellulose-synthesizing activity is successfully reconstituted in Escherichia coli by expressing the bacterial cellulose synthase complex of Gluconacetobacter xylinus: CesA and CesB (formerly BcsA and BcsB, respectively). Cellulose synthase activity was, however, only detected when CesA and CesB were coexpressed with diguanyl cyclase (DGC), which synthesizes cyclic-di-GMP (c-di-GMP), which in turn activates cellulose-synthesizing activity in bacteria. Direct observation by electron microscopy revealed extremely thin fibrillar structures outside E. coli cells, which were removed by cellulase treatment. This fiber structure is not likely to be the native crystallographic form of cellulose I, given that it was converted to cellulose II by a chemical treatment milder than ever described. We thus putatively conclude that this fine fiber is an unprecedented structure of cellulose. Despite the inability of the recombinant enzyme to synthesize the native structure of cellulose, the system described in this study, named “CESEC (CEllulose-Synthesizing E. Coli)”, represents a useful tool for functional analyses of cellulose synthase and for seeding new nanomaterials.Graphic Abstract <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/bomaf6/2014/bomaf6.2014.15.issue-11/bm501217g/production/images/medium/bm-2014-01217g_0008.gif'>
3
Pairing Symmetry in the Ordered Honeycomb Network Superconductor BaPtSb

Tsuyoshi Imazu,Masafumi Kudo,Shohei O. Singu,Jun Goryo,Yoshiki Imai 한국물리학회 2023 새물리 Vol.73 No.12
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We investigate the pairing symmetry of the ordered honeycomb network superconductor BaPtSb with broken inversion symmetry. There is a preliminary μSR measurement report below critical temperature (Tc) suggesting the superconducting state with time-reversal symmetry breaking (TRSB). In this paper, first principles calculation is performed and we find the effective tight-binding model which reproduces the Fermi surfaces consisting of Pt 5dx2-y2 , 5dxy and Sb 5pz orbitals mainly. In order to discuss the pairing symmetry of BaPtSb we classify the gap functions based on crystal point group and solve the gap equations, and the condensation energies are calculated. Consequently, on the most dominant Fermi surface, chiral d-wave state is most stable among the TRSB states.