825 research outputs found
Vortex density spectrum of quantum turbulence
The fluctuations of the vortex density in a turbulent quantum fluid are
deduced from local second-sound attenuation measurements. These measurements
are performed with a micromachined open-cavity resonator inserted across a flow
of turbulent He-II near 1.6 K. The power spectrum of the measured vortex line
density is compatible with a (-5/3) power law. The physical interpretation,
still open, is discussed.Comment: Submitted to Europhys. Let
Force measurements of a superconducting-film actuator for a cryogenic interferometric gravitational-wave detector
We measured forces applied by an actuator with a YBCO film at near 77 K for
the Large-scale Cryogenic Gravitational-wave Telescope (LCGT) project. An
actuator consisting of both a YBCO film of 1.6 micrometers thickness and 0.81
square centimeters area and a solenoid coil exerted a force of up to 0.2 mN on
a test mass. The presented actuator system can be used to displace the mirror
of LCGT for fringe lock of the interferometer.Comment: 9 pages, 3 figure
Theory of superconductivity of carbon nanotubes and graphene
We present a new mechanism of carbon nanotube superconductivity that
originates from edge states which are specific to graphene. Using on-site and
boundary deformation potentials which do not cause bulk superconductivity, we
obtain an appreciable transition temperature for the edge state. As a
consequence, a metallic zigzag carbon nanotube having open boundaries can be
regarded as a natural superconductor/normal metal/superconductor junction
system, in which superconducting states are developed locally at both ends of
the nanotube and a normal metal exists in the middle. In this case, a signal of
the edge state superconductivity appears as the Josephson current which is
sensitive to the length of a nanotube and the position of the Fermi energy.
Such a dependence distinguishs edge state superconductivity from bulk
superconductivity.Comment: 5 pages, 2 figure
Measurement of the mechanical loss of a cooled reflective coating for gravitational wave detection
We have measured the mechanical loss of a dielectric multilayer reflective
coating (ion-beam sputtered SiO and TaO) in cooled mirrors. The
loss was nearly independent of the temperature (4 K 300 K), frequency,
optical loss, and stress caused by the coating, and the details of the
manufacturing processes. The loss angle was . The
temperature independence of this loss implies that the amplitude of the coating
thermal noise, which is a severe limit in any precise measurement, is
proportional to the square root of the temperature. Sapphire mirrors at 20 K
satisfy the requirement concerning the thermal noise of even future
interferometric gravitational wave detector projects on the ground, for
example, LCGT.Comment: 8 pages, 6 figures, 3 tables : accepted version (by Physical Review
D
Absorption of Scintillation Light in a 100 Liquid Xenon Ray Detector and Expected Detector Performance
An 800L liquid xenon scintillation ray detector is being developed
for the MEG experiment which will search for decay
at the Paul Scherrer Institut. Absorption of scintillation light of xenon by
impurities might possibly limit the performance of such a detector. We used a
100L prototype with an active volume of 372x372x496 mm to study the
scintillation light absorption. We have developed a method to evaluate the
light absorption, separately from elastic scattering of light, by measuring
cosmic rays and sources. By using a suitable purification technique,
an absorption length longer than 100 cm has been achieved. The effects of the
light absorption on the energy resolution are estimated by Monte Carlo
simulation.Comment: 18 pages, 10 figures (eps). Submitted to Nucl. Instr. and Meth.
Electroluminescence of negatively charged single NV centers in diamond
The realization of electroluminescence (EL) of negatively charged nitrogen vacancy (NV−) centers is important toward all-electrical control of diamond quantum devices. In this study, we demonstrated electrical excitation and detection of EL of single NV⁻ centers by using lateral diamond p⁺–i(n⁻)–n⁺ diodes. It had been grown by homoepitaxy using the plasma enhanced chemical vapor deposition technique. We introduced a lightly phosphorus doped i(n⁻) layer to stabilize the negative state of NV centers. It was estimated that the efficiency of the electrical excitation rate of the NV center was more than 30 times enhanced by introducing lateral diamond p⁺–i(n⁻)–n⁺ diodes structure compared with the previous vertical diode. Furthermore, the EL of a single NV− center embedded in the i(n⁻) layer region was characterized. The results show that the charge state of the single NV centers can be manipulated by the voltage applied to the p⁺–i(n⁻)–n⁺ diode, where the emission of EL is increasingly dominated by NV⁻ in the range of 30 to 50 V
The Small Unit Cell Reconstructions of SrTiO3 (111)
We analyze the basic structural units of simple reconstructions of the (111)
surface of SrTiO3 using density functional calculations. The prime focus is to
answer three questions: what is the most appropriate functional to use; how
accurate are the energies; what are the dominant low-energy structures and
where do they lie on the surface phase diagram. Using test calculations of
representative small molecules we compare conventional GGA with higher-order
methods such as the TPSS meta-GGA and on-site hybrid methods PBE0 and TPSSh,
the later being the most accurate. There are large effects due to reduction of
the metal d oxygen sp hybridization when using the hybrid methods which are
equivalent to a dynamical GGA+U, which leads to rather substantial improvements
in the atomization energies of simple calibration molecules, even though the
d-electron density for titanium compounds is rather small. By comparing the
errors of the different methods we are able to generate an estimate of the
theoretical error, which is about 0.25eV per 1x1 unit cell, with changes of
0.5-1.0 eV per 1x1 cell with the more accurate method relative to conventional
GGA. An analysis of the plausible structures reveals an unusual low-energy
TiO2-rich configuration with an unexpected distorted trigonal biprismatic
structure. This structure can act as a template for layers of either TiO or
Ti2O3, consistent with experimental results as well as, in principle, Magnelli
phases. The results also suggest that both the fracture surface and the
stoichiometric SrTiO3 (111) surface should spontaneously disproportionate into
SrO and TiO2 rich domains, and show that there are still surprises to be found
for polar oxide surfaces.Comment: 14 pages, 4 Figure
Laser-Beam-Patterned Topological Insulating States on Thin Semiconducting MoS2
Identifying the two-dimensional (2D) topological insulating (TI) state in new materials and its control are crucial aspects towards the development of voltage-controlled spintronic devices with low-power dissipation. Members of the 2D transition metal dichalcogenides have been recently predicted and experimentally reported as a new class of 2D TI materials, but in most cases edge conduction seems fragile and limited to the monolayer phase fabricated on specified substrates. Here, we realize the controlled patterning of the 1T′ phase embedded into the 2H phase of thin semiconducting molybdenum-disulfide by laser beam irradiation. Integer fractions of the quantum of resistance, the dependence on laser-irradiation conditions, magnetic field, and temperature, as well as the bulk gap observation by scanning tunneling spectroscopy and theoretical calculations indicate the presence of the quantum spin Hall phase in our patterned 1T′ phasesThe work carried out at Aoyama Gakuin University was partly supported by a grant for
private universities and a Grant-in-Aid for Scientific Research (JP15K13277) awarded by MEXT. The work at the University of Tokyo was partly supported by Grantin-Aid for Scientific Research (JP17K05492, JP18H04218 and JP19H00652). J. J. P. and S. P. acknowledge Spanish MINECO through Grant No. FIS2016-80434-P, the Fundación Ramón Areces, the María de Maeztu Program for Units of Excellence in R&D (MDM-2014-
0377), the Comunidad Autónoma de Madrid through NANOMAGCOST Program, and the European Union Seventh Framework Programme under Grant Agreement
No. 604391 Graphene Flagship. S. P. acknowledges the computer resources and assistance provided by the Centro de Computación Científica of the Universidad Autónoma de Madrid. S. P. was also supported by the VILLUM FONDEN via the Center of Excellence for Dirac Materials (Grant No. 11744). D. M. and E. G.-M. gratefully
acknowledge support from the Graphene Flagship Graphene Core2 Contract No. 785219. E. G.-M also acknowledges IJCI-2017-32297 from Spanish MINECO/AE
Current status of the CLIO project
CLIO (Cryogenic Laser Interferometer Observatory) is a Japanese gravitational
wave detector project. One of the main purposes of CLIO is to demonstrate
thermal-noise suppression by cooling mirrors for a future Japanese project,
LCGT (Large-scale Cryogenic Gravitational Telescope). The CLIO site is in
Kamioka mine, as is LCGT. The progress of CLIO between 2005 and 2007 (room- and
cryogenic-temperature experiments) is introduced in this article. In a
room-temperature experiment, we made efforts to improve the sensitivity. The
current best sensitivity at 300 K is about
around 400 Hz. Below 20 Hz, the strain (not displacement) sensitivity is
comparable to that of LIGO, although the baselines of CLIO are 40-times shorter
(CLIO: 100m, LIGO: 4km). This is because seismic noise is extremely small in
Kamioka mine. We operated the interferometer at room temperature for
gravitational wave observations. We obtained 86 hours of data. In the cryogenic
experiment, it was confirmed that the mirrors were sufficiently cooled (14 K).
However, we found that the radiation shield ducts transferred 300K radiation
into the cryostat more effectively than we had expected. We observed that noise
caused by pure aluminum wires to suspend a mirror was suppressed by cooling the
mirror.Comment: 8 pages, 9 figures. Amaldi7 proceedings, J. Phys.: Conf. Ser.
(accepted
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