931 research outputs found
Work function of bulk-insulating topological insulator Bi2-xSbxTe3-ySey
Recent discovery of bulk insulating topological insulator (TI)
Bi2-xSbxTe3-ySey paved a pathway toward practical device application of TIs.
For realizing TI-based devices, it is necessary to contact TIs with a metal.
Since the band-bending at the interface dominates the character of devices,
knowledge of TIs' work function is of essential importance. We have determined
the compositional dependence of work function in Bi2-xSbxTe3-ySey by
high-resolution photoemission spectroscopy. The obtained work-function values
(4.95-5.20 eV) show a systematic variation with the composition, well tracking
the energy shift of the surface chemical potential seen by angle-resolved
photoemission spectroscopy. The present result serves as a useful guide for
developing TI-based electronic devices.Comment: 4pages, 2 figure
Direct Evidence for the Dirac-Cone Topological Surface States in Ternary Chalcogenide TlBiSe2
We have performed high-resolution angle-resolved photoemission spectroscopy
on TlBiSe2, which is a member of the ternary chalcogenides theoretically
proposed as candidates for a new class of three-dimensional topological
insulators. By measuring the energy band dispersions over the entire surface
Brillouin zone, we found a direct evidence for a non-trivial surface metallic
state showing a X-shaped energy dispersion within the bulk band gap. The
present result unambiguously establishes that TlBiSe2 is a strong topological
insulator with a single Dirac cone at the Brillouin-zone center. The observed
bulk band gap of 0.4 eV is the largest among known topological insulators,
making TlBiSe2 the most promising material for studying room-temperature
topological phenomena.Comment: 4 pages, 4 figure
Measurements of Stellar Inclinations for Kepler Planet Candidates II: Candidate Spin-Orbit Misalignments in Single and Multiple-Transiting Systems
We present a test for spin-orbit alignment for the host stars of 25 candidate
planetary systems detected by the {\it Kepler} spacecraft. The inclination
angle of each star's rotation axis was estimated from its rotation period,
rotational line broadening, and radius. The rotation periods were determined
using the {\it Kepler} photometric time series. The rotational line broadening
was determined from high-resolution optical spectra with Subaru/HDS. Those same
spectra were used to determine the star's photospheric parameters (effective
temperature, surface gravity, metallicity) which were then interpreted with
stellar-evolutionary models to determine stellar radii. We combine the new
sample with the 7 stars from our previous work on this subject, finding that
the stars show a statistical tendency to have inclinations near 90, in
alignment with the planetary orbits. Possible spin-orbit misalignments are seen
in several systems, including three multiple-planet systems (KOI-304, 988,
2261). Ideally these systems should be scrutinized with complementary
techniques---such as the Rossiter-McLaughlin effect, starspot-crossing
anomalies or asteroseismology---but the measurements will be difficult owing to
the relatively faint apparent magnitudes and small transit signals in these
systems.Comment: 11 pages, 9 figures, accepted for publication in Ap
Manipulation of Topological States and Bulk Band Gap Using Natural Heterostructures of a Topological Insulator
We have performed angle-resolved photoemission spectroscopy on
(PbSe)5(Bi2Se3)3m, which forms a natural multilayer heterostructure consisting
of a topological insulator (TI) and an ordinary insulator. For m = 2, we
observed a gapped Dirac-cone state within the bulk-band gap, suggesting that
the topological interface states are effectively encapsulated by block layers;
furthermore, it was found that the quantum confinement effect of the band
dispersions of Bi2Se3 layers enhances the effective bulk-band gap to 0.5 eV,
the largest ever observed in TIs. In addition, we found that the system is no
longer in the topological phase at m = 1, pointing to a topological phase
transition between m = 1 and 2. These results demonstrate that utilization of
naturally-occurring heterostructures is a new promising strategy for realizing
exotic quantum phenomena and device applications of TIs.Comment: 5 pages, 5 figure
Unexpected Dirac-Node Arc in the Topological Line-Node Semimetal HfSiS
We have performed angle-resolved photoemission spectroscopy on HfSiS, which
has been predicted to be a topological line-node semimetal with square Si
lattice. We found a quasi-two-dimensional Fermi surface hosting bulk nodal
lines, alongside the surface states at the Brillouin-zone corner exhibiting a
sizable Rashba splitting and band-mass renormalization due to many-body
interactions. Most notably, we discovered an unexpected Dirac-like dispersion
extending one-dimensionally in k space - the Dirac-node arc - near the bulk
node at the zone diagonal. These novel Dirac states reside on the surface and
could be related to hybridizations of bulk states, but currently we have no
explanation for its origin. This discovery poses an intriguing challenge to the
theoretical understanding of topological line-node semimetals.Comment: 5 pages, 4 figures (paper proper) + 2 pages, figures (supplemental
material
Vitamin D Affects Neuronal Peptides in Neurodegenerative Disease: Differences of V-D2 and V-D3 for Affinity to Amyloid-β and Scrapie Prion Protein In Vitro
The misfolding of neuronal peptides such as Aβ40/42 in Alzheimer’s disease and cellular prion protein in scrapie induce abnormal aggregation of the peptides in the brain. The seeding of peptides’ oligomers from monomers is the initial step to form molten-globule states before abnormal aggregation. Therefore, compounds targeting the step are useful to clarify the mechanisms underlying aggregation of the proteins and Vitamin D derivatives, which can interact with both Aβ40 and cellular prion protein; however they show different effects in the oligomerization step of the proteins. We discuss the different effects of Vitamin D2 and Vitamin D3 in the interaction with these peptides in brain
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