2,314 research outputs found
muSR study of the Cu-spin dynamics in the electron-doped high-Tc cuprate of Pr0.86LaCe0.14Cu1-y(Zn,Ni)yO4
Effects of the Zn- and Ni-substitution on the Cu-spin dynamics in the
electron-doped Pr0.86LaCe0.14Cu1-y(Zn,Ni)yO4+a-d with y = 0, 0.01, 0.02, 0.05
and different values of the reduced oxygen content d have been studied using
zero-field muon-spin-relaxation (muSR) measurements at temperatures down to 2
K. For the as-grown sample (d = 0, y = 0) and the sample with a very small d
value (d < 0.01, y = 0), a muon-spin precession due to long-range
antiferromagnetic order has been observed. On the other hand, no precession has
been observed for moderately oxygen-reduced samples (0.01 < d < 0.09). It has
been found that for all the samples of 0.01 < d < 0.09 the asymmetry A(t) (muSR
time spectrum) in the long-time region increases with decreasing temperature at
low temperatures, suggesting possible slowing-down of the Cu-spin fluctuations.
On the other hand, no significant difference between Zn- and Ni-substitution
effects on the slowing down of the Cu-spin fluctuations has been observed.Comment: 4 pages, 2 figures, Proceeding of 10th muSR conference 2005, to be
published in Physica
Absence of the impurity-induced magnetic order in the electron-doped high-T_c_ cuprates Pr_0.86_LaCe_0.14_Cu_1-y_(Zn, Ni)_y_O_4_
Zero-field muon-spin-relaxation measurements have been carried out in order
to investigate the Zn- and Ni-substitution effects on the Cu-spin dynamics in
the electron-doped Pr_0.86_LaCe_0.14_Cu_1-y_(Zn, Ni)_y_O_4+\alpa-\delta_ with y
= 0, 0.01, 0.02, 0.05 and different values of the reduced oxygen content
\delta(\delta \le 0.09). For the samples with y = 0 and very small \delta
values of \delta < 0.01, a muon-spin precession due to the formation of a
long-range antiferromagnetic order has been observed at low temperatures below
\~ 5 K. For the moderately oxygen-reduced samples of 0.01 \le \delta \le 0.09,
on the contrary, no muon-spin precession has been observed and the temperature
dependence of the spectra is similar to one another regardless of the y value.
That is, no impurity-induced slowing down of the Cu-spin fluctuations has been
detected, which is very different from the results of the hole-doped high-T_c_
cuprates. The reason is discussed.Comment: 13 pages, 2 figures, Proceedings of ISS2004 (to be published in
Physica C
Muon-spin-relaxation and magnetic-susceptibility studies of effects of the magnetic impurity Ni on the Cu-spin dynamics and superconductivity in La_2-x_Sr_x_Cu_1-y_Ni_y_O_4_ with x = 0.13
Effects of the magnetic impurity Ni on the Cu-spin dynamics and
superconductivity have been studied in La_2-x_Sr_x_Cu_1-y_Ni_y_O_4_ with x =
0.13 changing y finely up to 0.10. Compared with the case of the nonmagnetic
impurity Zn, it has been found from the muon-spin-relaxation measurements that
a large amount of Ni is required to stabilize a magnetic order of Cu spins.
However, the evolution toward the stabilization of the magnetic order with
increasing impurity concentration is qualitatively similar to each other. The
area of the non-superconducting and slowly fluctuating or static region of Cu
spins around Ni has been found to be smaller than that around Zn, suggesting
that the pinning of rather long-ranged dynamical spin correlation such as the
so-called dynamical stripe by Ni is weaker than that by Zn. This may be the
reason why Zn destroys the superconductivity in the hole-doped high-T_c_
cuprates more markedly than Ni.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev.
Strings in five-dimensional anti-de Sitter space with a symmetry
The equation of motion of an extended object in spacetime reduces to an
ordinary differential equation in the presence of symmetry. By properly
defining of the symmetry with notion of cohomogeneity, we discuss the method
for classifying all these extended objects. We carry out the classification for
the strings in the five-dimensional anti-de Sitter space by the effective use
of the local isomorphism between \SO(4,2) and \SU(2,2). We present a
general method for solving the trajectory of the Nambu-Goto string and apply to
a case obtained by the classification, thereby find a new solution which has
properties unique to odd-dimensional anti-de Sitter spaces. The geometry of the
solution is analized and found to be a timelike helicoid-like surface
Polarization Effects in Chargino Production at High Energy Colliders
We investigate the chargino production process
at high energy
colliders in the framework of the minimal supersymmetric
standard model (MSSM). Here the high energy beams are obtained by the
backward Compton scattering of the laser flush by the electron in the basic
linear TeV colliders. We consider the polarization of the laser photons as
well as the electron beams. Appropriate beam polarization could be effective to
enhance the cross section and for us to extract the signal from the dominant
background .Comment: 7 pages, latex , 3 figures are available upon reques
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.
Distinct Fe-induced magnetic states in the underdoped and overdoped regimes of La2-xSrxCu1-yFeyO4 revealed by muon spin relaxation
Zero-field and longitudinal-field muon-spin-relaxation measurements have been
performed in partially Fe-substituted La2-xSrxCu1-yFeyO4 in a wide range of
hole concentration, to investigate the magnetic state induced by the Fe
substitution recently suggested from the neutron-scattering measurements [Phys.
Rev. Lett. 107, 127002 (2011)]. It has been found that the magnetic transition
temperature is notably enhanced through the 1% Fe substitution in a wide range
of hole concentration where superconductivity appears in Fe-free La2-xSrxCuO4.
In the underdoped regime, the Fe-induced magnetic order can be understood in
terms of the concept of stripe pinning by Fe as in the case of the Zn-induced
one in La2-xSrxCu1-yZnyO4. In the overdoped regime, on the other hand, the
Fe-induced magnetic order is short-ranged, which is distinct from the stripes.
It is plausible that a spin-glass state of Fe spins derived from the
Ruderman-Kittel-Kasuya-Yosida interaction is realized in the overdoped regime,
suggesting a change of the ground state from the strongly correlated state to
the Fermi-liquid state with hole doping in La-214 high-Tc cuprates.Comment: 10 pages, 6 figures, accepted for publication in Phys. Rev.
Real Space Imaging of Spin Polarons in Zn Doped SrCu2(BO3)2
We report on the real space profile of spin polarons in the quasi
two-dimensional frustrated dimer spin system SrCu2(BO3)2 doped with 0.16% of
Zn. The 11B nuclear magnetic resonance spectrum exhibits 15 additional boron
sites near non-magnetic Zn impurities. With the help of exact diagonalizations
of finite clusters, we have deduced from the boron spectrum the distribution of
local magnetizations at the Cu sites with fine spatial resolution, providing
direct evidence for an extended spin polaron. The results are confronted with
those of other experiments performed on doped and undoped samples of
SrCu2(BO3)2.Comment: 9 pages, 11 figures, including supplemental materials. accepted for
publication in PR
Periodic Thermonuclear X-ray Bursts from GS 1826-24 and the Fuel Composition as a Function of Accretion Rate
We analyze 24 type I X-ray bursts from GS 1826-24 observed by the Rossi X-ray
Timing Explorer between 1997 November and 2002 July. The bursts observed
between 1997-98 were consistent with a stable recurrence time of 5.74 +/- 0.13
hr. The persistent intensity of GS 1826-24 increased by 36% between 1997-2000,
by which time the burst interval had decreased to 4.10 +/- 0.08 hr. In 2002
July the recurrence time was shorter again, at 3.56 +/- 0.03 hr. The bursts
within each epoch had remarkably identical lightcurves over the full approx.
150 s burst duration; both the initial decay timescale from the peak, and the
burst fluence, increased slightly with the rise in persistent flux. The
decrease in the burst recurrence time was proportional to Mdot^(-1.05+/-0.02)
(where Mdot is assumed to be linearly proportional to the X-ray flux), so that
the ratio alpha between the integrated persistent and burst fluxes was
inversely correlated with Mdot. The average value of alpha was 41.7 +/- 1.6.
Both the alpha value, and the long burst durations indicate that the hydrogen
is burning during the burst via the rapid-proton (rp) process. The variation in
alpha with Mdot implies that hydrogen is burning stably between bursts,
requiring solar metallicity (Z ~ 0.02) in the accreted layer. We show that
solar metallicity ignition models naturally reproduce the observed burst
energies, but do not match the observed variations in recurrence time and burst
fluence. Low metallicity models (Z ~ 0.001) reproduce the observed trends in
recurrence time and fluence, but are ruled out by the variation in alpha. We
discuss possible explanations, including extra heating between bursts, or that
the fraction of the neutron star covered by the accreted fuel increases with
Mdot.Comment: 9 pages, 6 figures, accepted by ApJ. Minor revisions following the
referee's repor
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