2,601 research outputs found
Magnetic measurements at pressures above 10 GPa in a miniature ceramic anvil cell for a superconducting quantum interference device magnetometer
A miniature ceramic anvil high pressure cell (mCAC) was earlier designed by
us for magnetic measurements at pressures up to 7.6 GPa in a commercial
superconducting quantum interference (SQUID) magnetometer [N. Tateiwa et al.,
Rev. Sci. Instrum. 82, 053906 (2011)]. Here, we describe methods to generate
pressures above 10 GPa in the mCAC. The efficiency of the pressure generation
is sharply improved when the Cu-Be gasket is sufficiently preindented. The
maximum pressure for the 0.6 mm culet anvils is 12.6 GPa when the Cu-Be gasket
is preindented from the initial thickness of 0.30 to 0.06 mm. The 0.5 mm culet
anvils were also tested with a rhenium gasket. The maximum pressure attainable
in the mCAC is about 13 GPa. The present cell was used to study YbCu2Si2 which
shows a pressure induced transition from the non-magnetic to magnetic phases at
8 GPa. We confirm a ferromagnetic transition from the dc magnetization
measurement at high pressure. The mCAC can detect the ferromagnetic ordered
state whose spontaneous magnetic moment is smaller than 1 mB per unit cell. The
high sensitivity for magnetic measurements in the mCAC may result from the the
simplicity of cell structure. The present study shows the availability of the
mCAC for precise magnetic measurements at pressures above 10 GPa
Limb-Brightened Jet of 3C 84 Revealed by the 43-GHz Very-Long-Baseline-Array Observation
We present a study of sub-pc scale radio structure of the radio galaxy 3C
84/NGC 1275 based on the Very Long Baseline Array (VLBA) data at 43 GHz. We
discover a limb-brightening in the "restarted" jet associated with the 2005
radio outburst. In the 1990s, the jet structure was ridge-brightening rather
than limb-brightening, despite the observations being done with similar angular
resolution. This indicates that the transverse jet structure has changed
recently. This change in the morphology shows an interesting agreement with the
-ray flux increase, i.e., the -ray flux in 1990s was at least
seven times lower than the current one. One plausible explanation for the
limb-brightening is the velocity structure of the jet in the context of the
stratified jet, which is a successful scenario to explain the -ray
emission in some active galactic nuclei (AGNs). If this is the case, the change
in apparent transverse structure might be caused by the change in the
transverse velocity structure. We argue the possibility that the transition
from ridge-brightening to limb-brightening is related to the -ray time
variability on the timescale of decades. We also discuss the collimation
profile of the jet.Comment: 22 pages, 4 figures, Accepted for Publication in Ap
Optical absorption spectra in SrCu_2O_3 two-leg spin ladder
We calculate the phonon-assisted optical-absorption spectra in SrCu_2O_3
two-leg spin-ladder systems. The results for two models proposed for SrCu_2O_3
are compared. In the model including the effects of a cyclic four-spin
interaction, the shoulder structure appears at 978 cm^{-1} and the peak appears
at 1975 cm^{-1} in the spectrum for polarization of the electric field parallel
to the legs. In the other model which describes a pure two-leg ladder, the peak
appears around the lower edge of the spectrum at 1344 cm^{-1}. The feature can
be effective in determining the proper model for SrCu_2O_3.Comment: 5 pages, 5 figures, to appear in PRB vol. 67 (2003
Dynamical structure factors of two-leg spin ladder systems
We investigate dynamical properties of two-leg spin ladder systems.
In a strong coupling region, an isolated mode appears in the lowest excited
states, while in a weak coupling region, an isolated mode is reduced and the
lowest excited states become a lower bound of the excitation continuum. We find
in the system with equal intrachain and interchain couplings that due to a
cyclic four-spin interaction, the distribution of the weights for the dynamical
structure factor and characteristics of the lowest excited states are strongly
influenced. The dynamical properties of two systems proposed for are also discussed.Comment: 5 pages, 6 figure
Magnetic structure, phase diagram, and a new type of spin-flop transition dominated by higher order interaction in a localized 5f system U3Pd20Si6
The magnetic structure of the localized-5f uranium intermetallic compound U3Pd20Si6 has been determined by means of a neutron diffraction experiment. Our data demonstrate that this compound has a collinear coupling of the sublattice ordering of the uranium spins on the 4a and 8c sites. We conclude that higher-order exchange and/or quadrupole interactions are necessary to stabilize this unique collinear structure. We discovered a new type of spin-flop transition against the uniaxial anisotropy induced by this collinear coupling
Pressure-induced Superconductivity in a Ferromagnet UGe -- Resistivity Measurements in Magnetic Field --
The electrical resistivity measurements in the magnetic field are carried out
on the pressure-induced superconductor UGe. The superconductivity is
observed from 1.06 to 1.44 GPa. The upper critical field of is
anisotropic where exhibits positive curvature for and
-axis. The characteristic enhancement of is reconfirmed for
-axis. In the temperature and field dependence of resistivity at where the ferromagnetic ordering disappears, it is observed that the
application of the external field along the {\it a}-axis increases the
coefficient of Fermi liquid behavior correspondingly to the
metamagnetic transition.Comment: To be published in the proceeding of the International Conference on
High Pressure Science and Technology(AIRAPT-18),Beijing,China,23-27 July 200
Flux Line Lattice Melting and the Formation of a Coherent Quasiparticle Bloch State in the Ultraclean URuSi Superconductor
We find that in ultraclean heavy-fermion superconductor URuSi
( K) a distinct flux line lattice melting transition with
outstanding characters occurs well below the mean-field upper critical fields.
We show that a very small number of carriers with heavy mass in this system
results in exceptionally large thermal fluctuations even at subkelvin
temperatures, which are witnessed by a sizable region of the flux line liquid
phase. The uniqueness is further highlighted by an enhancement of the
quasiparticle mean free path below the melting transition, implying a possible
formation of a quasiparticle Bloch state in the periodic flux line lattice.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Let
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