We have performed a high-resolution angle-resolved photoelectron spectroscopy study on the newly discovered superconductor Ba0.6K0.4Fe2As2 (Tc = 37 K). We have observed two superconducting gaps with different values: a large gap (∆ ∼ 12 meV) on the two small holelike and electron-like Fermi surface (FS) sheets, and a small gap (∼ 6 meV) on the large hole-like FS. Both gaps, closing simultaneously at the bulk transition temperature (Tc), are nodeless and nearly isotropic around their respective FS sheets. The isotropic pairing interactions are strongly orbital dependent, as the ratio 2∆/kBTc switches from weak to strong coupling on different bands. The same and surprisingly large superconducting gap due to strong pairing on the two small FSs, which are connected by the (π, 0) spin-density-wave vector in the parent compound, strongly suggests that the pairing mechanism originates from the inter-band interactions between these two nested FS sheets.

The three-dimensional topological insulator is a quantum state of matter characterized by an insulating bulk state and gapless Dirac cone surface states. Device applications of topological insulators require a highly insulating bulk and tunable Dirac carriers, which has so far been difficult to achieve. Here we demonstrate that Bi 2-x sb x Te 3-y se y is a system that simultaneously satisfies both of these requirements. For a series of compositions presenting bulk-insulating transport behaviour, angle-resolved photoemission spectroscopy reveals that the chemical potential is always located in the bulk band gap, whereas the Dirac cone dispersion changes systematically so that the Dirac point moves up in energy with increasing x, leading to a sign change of the Dirac carriers at x~0.9. such a tunable Dirac cone opens a promising pathway to the development of novel devices based on topological insulators.

We developed highly efficient fluorescent dopants for full‐color OLEDs. For blue, green and red OLEDs, current efficiencies of 8.7cd/A, 20.5 cd/A and 11.4 cd/A at 10mA/cm2 were achieved, respectively. Lifetime of the blue device was estimated to be 23,000hours at an initial luminance of 1,000 cd/m2. Moreover, long lifetime of 100,000 hours was estimated in the green and red devices. By the use of these dopants, we expect that a full‐color OLED display with the lifetime of 18,000 hours at a white luminance of 300 cd/m2 can be achieved.

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We have performed systematic ultrahigh-resolution photoemission spectroscopy on the ironbased superconductor LaFeAsO1−xFx (x = 0-14%) to elucidate the evolution of electronic states with doping. We found that the density of states (DOS) around the Fermi level of the superconducting sample is markedly smaller than that of the undoped sample in contrast to conventional phonon-mediated superconductors. We observed a pseudogap in the DOS above the superconducting transition temperature (Tc) which opens/closes at a temperature (T *) well above Tc. The energy scale of pseudogap and the T * value are gradually reduced upon fluorine substitution. The origin of pseudogap is discussed in terms of the partial nesting of Fermi surfaces due to the spin-density-wave formation or the short-range spin correlations.

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