334 research outputs found
Atomic displacements and lattice distortion in the magnetic-field-induced charge ordered state of SmRuP
Structural properties of SmRuP in the anomalous magnetic ordered
phase between K and K in magnetic fields has
been studied by x-ray diffraction. Atomic displacements of Ru and P, reflecting
the field-induced charge order of the electrons, have been deduced by
analyzing the intensities of the forbidden Bragg peaks, assuming a cubic space
group . Also, by utilizing high-resolution x-ray diffraction
experiment, we observed a splitting of fundamental Bragg peaks, clarifying that
the unit cell in the magnetic ordered phase is rhombohedral elongated along the
axis. Responses of the rhombohedral domains to the magnetic
field, which reflects the direction of the magnetic moment, is studied in
detail.Comment: 11 pages, 11 figures, accepted for publication in PR
Prospects for improving the sensitivity of KAGRA gravitational wave detector
KAGRA is a new gravitational wave detector which aims to begin joint observation with Advanced LIGO and Advanced Virgo from late 2019. Here, we present KAGRA's possible upgrade plans to improve the sensitivity in the decade ahead. Unlike other state-of-the-art detectors, KAGRA requires different investigations for the upgrade since it is the only detector which employs cryogenic cooling of the test mass mirrors. In this paper, investigations on the upgrade plans which can be realized by changing the input laser power, increasing the mirror mass, and injecting frequency dependent squeezed vacuum are presented. We show how each upgrade affects to the detector frequency bands and also discuss impacts on gravitational-wave science. We then propose an effective progression of upgrades based on technical feasibility and scientific scenarios
YbPtPb: Magnetic frustration in the Shastry-Sutherland lattice
We have synthesized single crystals of YbPtPb, which crystallize
in the layered UPtSn-type structure, where planes of Yb ions lie on
a triangular network. We report here the first results of magnetization,
specific heat, and electrical resistivity experiments. The lattice constants
and high temperature magnetic susceptibility indicate that the Yb ions are
trivalent, while Schottky peaks in the specific heat show that the ground state
is a well isolated doublet. Significant magnetic anisotropy is observed, with
the ratio of susceptibilities perpendicular and parallel to the magnetic planes
differing by as much as a factor of 30 at the lowest temperatures.
Antiferromagnetic order occurs at a N\'eel temperature =2.07 K, a
transition temperature which is more than an order of magnitude smaller than
the mean field interactions reflected by the in-plane Weiss temperature.
Further evidence for short ranged magnetic fluctuations is found in the
magnetic susceptibility and electrical resistivity, which have broad peaks
above , and in the slow development of the magnetic entropy at
. Our experiments indicate that YbPtPb is a quasi-two
dimensional and localized moment system, where strong magnetic frustration may
arise from the geometry of the underlying Shastry-Sutherland lattice.Comment: 8 pages, 8 figure
Exact solution of the geometrically frustrated spin-1/2 Ising-Heisenberg model on the triangulated Kagome (triangles-in-triangles) lattice
The geometric frustration of the spin-1/2 Ising-Heisenberg model on the
triangulated Kagome (triangles-in-triangles) lattice is investigated within the
framework of an exact analytical method based on the generalized star-triangle
mapping transformation. Ground-state and finite-temperature phase diagrams are
obtained along with other exact results for the partition function, Helmholtz
free energy, internal energy, entropy, and specific heat, by establishing a
precise mapping relationship to the corresponding spin-1/2 Ising model on the
Kagome lattice. It is shown that the residual entropy of the disordered spin
liquid phase is for the quantum Ising-Heisenberg model significantly lower than
for its semi-classical Ising limit (S_0/N_T k_B = 0.2806 and 0.4752,
respectively), which implies that quantum fluctuations partially lift a
macroscopic degeneracy of the ground-state manifold in the frustrated regime.
The investigated model system has an obvious relevance to a series of polymeric
coordination compounds Cu_9X_2(cpa)_6 (X=F, Cl, Br and cpa=carboxypentonic
acid) for which we made a theoretical prediction about the temperature
dependence of zero-field specific heat.Comment: 13 pages, 7 figures, submitted to Phys. Rev.
Current status of space gravitational wave antenna DECIGO and B-DECIGO
Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is the future Japanese space mission with a frequency band of 0.1 Hz to 10 Hz. DECIGO aims at the detection of primordial gravitational waves, which could be produced during the inflationary period right after the birth of the universe. There are many other scientific objectives of DECIGO, including the direct measurement of the acceleration of the expansion of the universe, and reliable and accurate predictions of the timing and locations of neutron star/black hole binary coalescences. DECIGO consists of four clusters of observatories placed in the heliocentric orbit. Each cluster consists of three spacecraft, which form three Fabry-Perot Michelson interferometers with an arm length of 1,000 km. Three clusters of DECIGO will be placed far from each other, and the fourth cluster will be placed in the same position as one of the three clusters to obtain the correlation signals for the detection of the primordial gravitational waves. We plan to launch B-DECIGO, which is a scientific pathfinder of DECIGO, before DECIGO in the 2030s to demonstrate the technologies required for DECIGO, as well as to obtain fruitful scientific results to further expand the multi-messenger astronomy
KAGRA: 2.5 Generation Interferometric Gravitational Wave Detector
The recent detections of gravitational waves (GWs) reported by LIGO/Virgocollaborations have made significant impact on physics and astronomy. A globalnetwork of GW detectors will play a key role to solve the unknown nature of thesources in coordinated observations with astronomical telescopes and detectors.Here we introduce KAGRA (former name LCGT; Large-scale Cryogenic Gravitationalwave Telescope), a new GW detector with two 3-km baseline arms arranged in theshape of an "L", located inside the Mt. Ikenoyama, Kamioka, Gifu, Japan.KAGRA's design is similar to those of the second generations such as AdvancedLIGO/Virgo, but it will be operating at the cryogenic temperature with sapphiremirrors. This low temperature feature is advantageous for improving thesensitivity around 100 Hz and is considered as an important feature for thethird generation GW detector concept (e.g. Einstein Telescope of Europe orCosmic Explorer of USA). Hence, KAGRA is often called as a 2.5 generation GWdetector based on laser interferometry. The installation and commissioning ofKAGRA is underway and its cryogenic systems have been successfully tested inMay, 2018. KAGRA's first observation run is scheduled in late 2019, aiming tojoin the third observation run (O3) of the advanced LIGO/Virgo network. In thiswork, we describe a brief history of KAGRA and highlights of main feature. Wealso discuss the prospects of GW observation with KAGRA in the era of O3. Whenoperating along with the existing GW detectors, KAGRA will be helpful to locatea GW source more accurately and to determine the source parameters with higherprecision, providing information for follow-up observations of a GW triggercandidate
Vibration isolation system with a compact damping system for power recycling mirrors of KAGRA
A vibration isolation system called the Type-Bp system used for power recycling mirrors has been developed for KAGRA, the interferometric gravitational-wave observatory in Japan. A suspension of the Type-Bp system passively isolates an optic from seismic vibration using three main pendulum stages equipped with two vertical vibration isolation systems. A compact reaction mass around each of the main stages allows for achieving sufficient damping performance with a simple feedback as well as vibration isolation ratio. Three Type-Bp systems were installed in KAGRA, and were proved to satisfy the requirements on the damping performance, and also on estimated residual displacement of the optics
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