322 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
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Surface tension measurement of glass melts by the maximum bubble pressure method
The maximum bubble pressure method was used to obtain accurate surface tension measurements. The dependence of apparent surface tension value on bubble growth time was measured for times from several to longer than a thousand seconds. The static surface tension value was obtained by extrapolating bubble growth time to infinity. The dynamic surface tension, which is familiar in colloids, could not be directly obtained because of the high viscosity of glass melt. The effects of capillary tip material and shape were also examined. This method is applicable to melts with viscosity less than 10^3.5 dPa s. The reproducibility in the measurement was within a few percent
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
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