948 research outputs found
Surface Shubnikov-de Hass oscillations and non-zero Berry phases of the topological hole conduction in TlBiSe
We report the observation of two-dimensional Shubnikov-de Hass (SdH)
oscillations in the topological insulator TlBiSe. Hall
effect measurements exhibited electron-hole inversion in samples with bulk
insulating properties. The SdH oscillations accompanying the hole conduction
yielded a large surface carrier density of /cm, with the Landau-level fan diagram exhibiting the
Berry phase. These results showed the electron-hole reversibility around the
in-gap Dirac point and the hole conduction on the surface Dirac cone without
involving the bulk metallic conduction.Comment: 5 pages, 4 figure
Precise determination of two-carrier transport properties in the topological insulator TlBiSe
We report the electric transport study of the three-dimensional topological
insulator TlBiSe. We applied a newly developed analysis procedure and
precisely determined two-carrier transport properties. Magnetotransport
properties revealed a multicarrier conduction of high- and low-mobility
electrons in the bulk, which was in qualitative agreement with angle-resolved
photoemission results~[K. Kuroda , Phys. Rev. Lett. , 146801
(2010)]. The temperature dependence of the Hall mobility was explained well
with the conventional Bloch-Gr{\"u}neisen formula and yielded the Debye
temperature ~K. The results indicate that the
scattering of bulk electrons is dominated by acoustic phonons.Comment: 6 pages, 5 figures, to be published in Physical Review
Photon correlation in GaAs self-assembled quantum dots
We report on photon coincidence measurement in a single GaAs self-assembled
quantum dot (QD) using a pulsed excitation light source. At low excitation,
when a neutral exciton line was present in the photoluminescence (PL) spectrum,
we observed nearly perfect single photon emission from an isolated QD at 670 nm
wavelength. For higher excitation, multiple PL lines appeared on the spectra,
reflecting the formation of exciton complexes. Cross-correlation functions
between these lines showed either bunching or antibunching behavior, depending
on whether the relevant emission was from a biexciton cascade or a charged
exciton recombination.Comment: 5 pages, 3 figure
Adsorption enhancement of nitrogen gas by atomically heterogeneous nanospace of boron nitride
In this study, porous boron nitride (p-BN) with hexagonal phase boron nitride (h-BN) pore walls was synthesized using high-temperature calcination. Negligible variation in pore-wall structure can be observed in powder X-ray diffraction (XRD) profiles and infrared (IR) spectra. However, a highly stable p-BN with a stable pore structure even at 973 K under the oxidative conditions is obtained when synthesized at higher than 1573 K under nitrogen gas flow. For p-BN, this stability is obtained by generating h-BN microcrystals. Nitrogen adsorption–desorption isotherms at 77 K provide type-IV features and typical adsorption–desorption hysteresis, which suggests micropore and mesopore formation. Moreover, adsorption–desorption isotherms of Ar at 87 K are measured and compared with those of nitrogen. The relative adsorbed amount of nitrogen (i.e., the amount of nitrogen normalized by that of Ar at each relative pressure or adsorption potential value) on p-BN is considerably larger than that on microporous carbon at low-pressure regions, which suggests the existence of strong adsorption sites on the p-BN surface. In fact, the relative number of adsorbed nitrogen molecules to that of Ar on p-BN is, at most, 150%–200% larger than that on microporous carbon for the same adsorption potential state. Furthermore, additional adsorption enhancement to nitrogen between P/P0 = 10−5 and 10−3 can be observed for p-BN treated at 1673 K, which suggests the uniformly adsorbed layer formation of nitrogen molecules in the vicinity of a basal planar surface. Thus, unlike typical nanoporous sp2 carbons, p-BN materials have the potential to enhance adsorption for certain gas species because of their unique surface state
Conduction Effect of Thermal Radiation in a Metal Shield Pipe in a Cryostat for a Cryogenic Interferometric Gravitational Wave Detector
A large heat load caused by thermal radiation through a metal shield pipe was
observed in a cooling test of a cryostat for a prototype of a cryogenic
interferometric gravitational wave detector. The heat load was approximately
1000 times larger than the value calculated by the Stefan-Boltzmann law. We
studied this phenomenon by simulation and experiment and found that it was
caused by the conduction of thermal radiation in a metal shield pipe.Comment: 7 pages, 4 figures, 2 tables, Submitted to Jpn. J. Appl. Phy
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