51,857 research outputs found
Hole-trapping by Ni, Kondo effect and electronic phase diagram in non-superconducting Ni-substituted La2-xSrxCu1-yNiyO4
In order to investigate the electronic state in the normal state of high-Tc
cuprates in a wide range of temperature and hole-concentration, specific-heat,
electrical-resistivity, magnetization and muon-spin-relaxation (muSR)
measurements have been performed in non-superconducting Ni-substituted
La2-xSrxCu1-yNiyO4 where the superconductivity is suppressed through the
partial substitution of Ni for Cu without disturbing the Cu-spin correlation in
the CuO2 plane so much. In the underdoped regime, it has been found that there
exist both weakly localized holes around Ni and itinerant holes at high
temperatures. With decreasing temperature, all holes tend to be localized,
followed by the occurrence of variable-range hopping conduction at low
temperatures. Finally, in the ground state, it has been found that each Ni2+
ion traps a hole strongly and that a magnetically ordered state appears. In the
overdoped regime, on the other hand, it has been found that a Kondo-like state
is formed around each Ni2+ spin at low temperatures. In conclusion, the ground
state of non-superconducting La2-xSrxCu1-yNiyO4 changes upon hole doping from a
magnetically ordered state with the strong hole-trapping by Ni2+ to a metallic
state with Kondo-like behavior due to Ni2+ spins, and the quantum phase
transition is crossover-like due to the phase separation into short-range
magnetically ordered and metallic regions.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.
Alfv\'en wave-driven wind from RGB and AGB stars
We develop a magnetohydrodynamical model of Alfv\'en wave-driven wind in open
magnetic flux tubes piercing the stellar surface of Red Giant Branch (RGB) and
Asymptotic Giant Branch (AGB) stars, and investigate the physical properties of
the winds. The model simulations are carried out along the evolutionary tracks
of stars with initial mass in the range of 1.5 to 3.0 and initial
metallicity =0.02. The surface magnetic field strength being set
to be 1G, we find that the wind during the evolution of star can be classified
into the following four types; the first is the wind with the velocity higher
than 80 km s in the RGB and early AGB (E-AGB) phases; the second is the
wind with outflow velocity less than 10 km s seen around the tip of RGB
or in the E-AGB phase; the third is the unstable wind in the E-AGB and
thermally pulsing AGB (TP-AGB) phases; the fourth is the stable massive and
slow wind with the mass-loss rate higher than 10 yr and
the outflow velocity lower than 20 km s in the TP-AGB phase. The
mass-loss rates in the first and second types of wind are two or three orders
of magnitude lower than the values evaluated by an empirical formula. The
presence of massive and slow wind of the fourth type suggests the possibility
that the massive outflow observed in TP-AGB stars could be attributed to the
Alfv\'en wave-driven wind.Comment: 17 pages, 15 figures, accepted for publication in Ap
Development of Cu-spin correlation in Bi_1.74_Pb_0.38_Sr_1.88_Cu_1-y_Zn_y_O_6+d_ high-temperature superconductors observed by muon spin relaxation
A systematic muon-spin-relaxation study in Bi-2201 high-Tc cuprates has
revealed for the first time that the Cu-spin correlation (CSC) is developed at
low temperatures below 2 K in a wide range of hole concentration where
superconductivity appears. The CSC tends to become weak gradually with
increasing hole-concentration. Moreover, CSC has been enhanced through the 3%
substitution of Zn for Cu. These results are quite similar to those observed in
La-214 high-Tc cuprates. Accordingly, it has been suggested that the intimate
relation between the so-called spin-charge stripe correlations and
superconductivity is a universal feature in hole-doped high-Tc cuprates.
Furthermore, apparent development of CSC, which is suppressed through the Zn
substitution oppositely, has been observed in non-superconducting heavily
overdoped samples, being argued in the context of a recently proposed
ferromagnetic state in heavily overdoped cuprates.Comment: 6 pages, 5 figure
Lattice monopole action in pure SU(3) QCD
We obtain an almost perfect monopole action numerically after abelian
projection in pure SU(3) lattice QCD. Performing block-spin transformations on
the dual lattice, the action fixed depends only on a physical scale b. Monopole
condensation occurs for large b region. The numerical results show that
two-point monopole interactions are dominant for large b. We next perform the
block-spin transformation analytically in a simplified case of two-point
monopole interactions with a Wilson loop on the fine lattice. The perfect
operator evaluating the static quark potential on the coarse b-lattice are
derived. The monopole partition function can be transformed into that of the
string model. The static potential and the string tension are estimated in the
string model framework. The rotational invariance of the static potential is
recovered, but the string tension is a little larger than the physical one.Comment: 21pages,4figures,to be published in JHE
Topological Charge of Lattice Abelian Gauge Theory
Configuration space of abelian gauge theory on a periodic lattice becomes
topologically disconnected by excising exceptional gauge field configurations.
It is possible to define a U(1) bundle from the nonexceptional link variables
by a smooth interpolation of the transition functions. The lattice analogue of
Chern character obtained by a cohomological technique based on the
noncommutative differential calculus is shown to give a topological charge
related to the topological winding number of the U(1) bundle.Comment: 20 pages, latex, nofigur
Observation of EAS using a large water tank
Using a large water tank (30 m in diameter, 4.5 m in depth) transition of extensive air showers (EAS) was investigated at Taro (200 m above sea level). There are set 150,0.4 sq m proportional counters on the bottom of the water tank. A conventional EAS array of 25 plastic scintillation detectors was arranged within several tens meter from the water tank. A proportional counter (10x10x200 cc x2) is made of a square shaped pipe of iron. Tungsten wire (100 mu m phi) is stretched tight in the center of the counter. A gas mixture of 90% argon and 10% methane is used at 760 mmHg. About 3000 EAS were obtained through 1 m of water since 1984
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